The great floral feature at the Centennial for May was Mr. Waterer's Rhododendrons. A house was built for these by the Centennial authorities, like a huge curvilinear conservatory, only covered with canvas instead of glass. Mr. Waterer arranged the ground inside in what is known to gardeners as the "Regent's Park style." In some places the earth was raised so as to be several feet above the natural level, forming a "bluff," around which a walk would be led, and then again were levels and rises, with narrow grass verges and broad, sanded walks, the Rhododendrons thickly planted in the beds, and the whole forming a delightful piece of landscape gardening. There were fifteen hundred plants in about eighty varieties in the collection, and we think it is safe to say that nothing ever exhibited in a floral way in the United States attracted so much attention or received such unqualified admiration. The house was crowded from morning to evening, and many visitors who found themselves unexpectedly among so much floral beauty telegraphed to their distant friends to come right on, and see the glorious sight.

It was evident that although all the leading American nurserymen have been for years endeavoring to introduce Rhododendron culture, not one in a hundred of the thousands of visitors here ever saw one before, and the influence on their introduction will be immense.

But not only to the great multitude was this a great lesson, but all of us found much to learn from the great exhibit of so many varieties all blooming here together. We fancy that few ever took into consideration how great is the diversity of form and habit among these plants, as well as in the form, color and markings of the flowers; yet to those making collections of these beautiful things such points will enter largely into the system of selection. Some make long straggling growths, while others have a dense, compact habit. Some kinds perhaps making specimens four or five feet high would have but a dozen or so of heads of flowers, while other varieties would have half a hundred in plants of the same size. Then there is a great difference in the shape of the heads - some kinds having them as round as an orange, and others cone-like, as in a pine-apple. Some kinds have rather short pedicels to the flowers, and then the head is compact, while others are long, and then the head is loose. So in number. There are kinds which will have nearly double the quantity of flowers in a head that others will.

All these and similar points enter largely into the sum total of pleasure to be derived from a collection of Rhododendrons, and no doubt many of them were noted in the memorandum books of the visitors, which we were pleased to see in common use.

It is generally known that the Rhododendron is an "American plant," and people wonder why Americans cannot grow one of their own articles as good as Europeans. It is not as generally known that these garden forms are hybrids between the American species and the Rhododendron ponticum, and perhaps in some cases R. arboreum, which have ft much tenderer constitution, and hence where this "sap" predominates, the plants are not hardy enough for an average North American winter. The American R. maximum is found wild as far north as Nova Scotia. The Catawbiense flourishes in the cold mountains of North Carolina. If these two alone were concerned in these hybrids we should have a true stock of " American plants." The seed of the Rhododendron is as fine as dust; and only those skilled in seed raising can grow the plants in this way. It has to be strewn on or very near the surface, and the atmosphere kept so moist that very little watering to disturb the seed will be required. After getting the plants, if peculiar kinds are to be perpetuated, they have to be grafted, and this adds to the expense. Seedlings not grafted, are generally beautiful enough for the average grower.

They have a good variety of color and form among them.

As a matter of culture it may be noted that the roots are extremely delicate and hair-like; and as roots must have air, the plants must be kept very near the surface in the average heavy soils of our country. Where the soil is of a loose, sandy, stony, or peaty character, full of air spaces, this precaution is of no consequence. The Rhododendron seems also to have an antipathy to lime. Those varieties which are of the hardiest are still much benefited by a shelter of trees or bushes from the windward quarter. If they have this protection, and the precautions we have suggested be taken in regard to keeping the little roots near the surface and in cool, open soil, it makes little difference whether they be grown in the sun or the shade.

These and similar questions were plied us while we were taking notes in Waterer's tent, so we thought we might just as well incorporate the answers we had to give in this notice here. Often it was observed to us, "So many look alike; which are the most distinct?" In answer we give the following, without, however, being able to say that they are the best selection for standing our severe climate. That can be only a matter for experiment, though some, as for instance Everestianum, are known to do well.

Album grandiflorum - very large dense heads of lilac and white.

Everestianum - a dense grower, free bloomer; flowers rosy pink, with crimped edges.

Archimedes - rose white, small, but numerous heads.

Album elegans - rosy white; heads not numerous, but large and conical.

Titian - rose shaded white; rather loose habit of growth, but very showy.

• Lady Eleanor Cathcart - one of the most attractive, rosy flowers, with dark spots on the upper petals; heads compact and numerous.

John Waterer - deep vermilion rose; one might say as good as some Rhododendron arbor-eum's. Rather diffuse in habit.

Queen - delicate rosy white. The great charm of this is in its rounded lobes of the corolla; almost as perfect in this respect as the Camellia.

Mrs. Halford-has very large heads, with diffuse habit.

Vandyke - small dense heads of purple crimson flowers.

Minnie - small heads, rosy white, with yellowish green spots on the upper petal; an easy, free, rapid grower.

Lady Cathcart - a superb variety, looking as if the heads of flowers were made up of the old-fashioned Pelargoniums, before we had to mix up geraniums with them.

Then we noted as possessing points of special merit as distinct Archimedes, Fastuosum pleno, Michael Waterer, Lady Armstrong, Mrs. John Waterer, Stella, Lady Cleremont, Concessum, King of the Purples, John Marshall Brooks, and Mrs. John Chitton.

Desirous of knowing how far those we selected, as the most distinct of the collection as we saw them in bloom, would come out in a contest with the whole of the collection as Mr. Waterer knew them, we asked him for a list of six of those he would consider the most distinct, whether in flower are not, and these are they: Everestiana, Mrs. John Chitton, John Waterer, Lees Purple, Charles Dickens, and Titian. It was a great pleasure to note that one who came so far to exhibit at this great exposition did his part so well, and that his efforts were so highly appreciated.

We went from here to the open grounds, where the two firms of Parsons, of Flushing, had made grand exhibitions of Rhododendrons also. If they had had a house given to them as the commission gave one to Mr. Waterer, or if only a part of the house had been given to Mr. Waterer and a part to the two Parsons, there would have been a fair chance of a competitive comparison. The Parsons' collections in the open ground had apparently a greater number of fine specimens than the Waterer collection, and perhaps as many varieties, but of course had no competitive chance whatever with those in the house to make a public impression. In fact not one in a thousand who saw and admired the Waterer collection know now that the Messrs. Parsons had any at all on the grounds. It is pleasant to be able to say that, notwithstanding the immense disadvantage the American Rhododendron firms were placed under, we have not heard one word of complaint from the Messrs. Parsons - nothing but pleasure that our English friends who came so far with their productions should be treated so well.

It was our intention to do these excellent firms some justice by making notes of their good things. On getting to their department we were astonished at being ordered away by the guards, and we found by further experiment that this was the " law." We made an effort to examine the collection of Messrs. Hoopes, the Roses of Mr. Buist, the Geraniums of Peter Henderson, and finally the Arboretum planted by the writer of this, and was ordered away from all! On suggesting to the official seraph, who held the flaming sword at the gate, that surely one had a right to enter his own Eden, we were told that he " was not supposed to know exhibitors from other people." But we were fighting rather for " other people" than our-selves. We addressed a letter to Director General Goshorn, pointing out that the exhibitors in the open ground planted their allotments for people to examine the varieties, and not as mere masses of flowers and foliage for the landscape adornment of the Centennial grounds, and expressing a hope that the wrong would be remedied.

We had not the honor of a reply from any one in authority, but just as we go to press with this find by experience that the guards have been withdrawn, and that the public now are as free to examine the Horticultural collections as any other on the grounds.

These remarks are necessary in order to explain to our readers why we are unable to give any account of the out-door flowers, and to correct the impression carried naturally through the country by those Horticulturists who during the first month were ordered away, that the collections can only be seen from a distance varying from 10 to 50 feet off. This difficulty does not exist now, and we hope to have a clear field for reporting in the future. Any one can go on the grass to examine the collections.