The Twbnty-seventh Annual Exhibition of the Pennsylvania Horticultural Society, was held in Philadelphia on the 11th, 12th, and 13th of September. As no hall could be found large enough to accommodate the Society, the City Councils of Philadelphia very liberally granted them the use of one of the Public Squares, and in it the Society have made one of the most brilliant displays our city has ever witnessed. The whole square was covered with canvas tents and marquees, so as entirely to cover the trees growing in it - while to prevent any injury to the public property, the whole surface of the ground was planked over ; gas and water were introduced at great expense, and every effort made to render the exhibition worthy of our Horticultural farmers. That the exertions of the Society were eminently successful, was attested by the continuous streams of human beings that poured in and out during the whole period of three days and evenings. It was estimated by good judges that not less than 30,000 persons must have attended the Fair.

All that we can do in this place to interest the general reader, is to give a few notes of anything that strikes us as novel or interesting.

A specimen of Nymphaea Cerulea, a water plant with blue flowers about 6 inches across, was very attractive. It is of very easy culture, and does well in the open air in summer - a leaf of the Victoria Regia was placed near it, but no flower. The pretty Bouvardia long-iflora, seen here for the first time, gives promise of being a valuable introduction. It has large white flowers, in size, shape, and odor, resembling the common Jessamine. Weigela, or rather Diervilla amabilis, was also in flower ; this, though something like D. japonica, (W. rosea,) will always be prized for its constant blooming property. Begonia umbilicata, a very pretty individual of the herbaceous section, with brilliant scarlet vermillion flowers, and leaves pretty much of the same hue. Eranthemum leuco-nervum, not exactly new, but very striking by its white veined foliage. Coleus Blumeii, though now rather common in Philadelphia collections, was much admired for its finely variegated foliage, as also were Tillandsia Zebrina, Hydrangea hortensis variegata, Echites nutans, Dioscorea variegata, Maranta vittata, and M. albo-lineata. In the same class of variegated plants, we saw for the first time, Aphelandra Leopold!!, a stove plant, and very pretty.

The competition for the best twenty specimens of plants in pots, was very brisk; there being no less than six entries, besides the exhibitors in the class of 12 and 6.

The Allamandas were in most collections, showing how popular they are with plant-growers. Stignaphyllon cilicetum, Begona Xanthina, Bouvardia Leiantha, the Clerodend-rons and Mannettias, also seem to be employed extensively to make good displays.

The display of Dahlias was very good, but the exhibitors having named their flowers on loose strips of paper, which every little breeze carried around the tents, they lost much of their interest with the fanciers.

The Orohideous plants were not as numerous this season as they have been in former years. Odontaglossum grande, was the best present, and is one of the very finest aerial orchids grown.

A collection of China Asters exhibited, was the theme of universal admiration. The poor "Queen Margaret's" have fallen into something like neglect with cultivators, during the past few years ; such fine specimens as these go far to resuscitate them.

The fruit department was as usual with our Society's exhibitors, brilliantly sustained. Amongst the novelties, we noticed fine specimens of tho Philadelphia pear, for it is a rarity now with us ; good specimens of the white Doyenne or Butter pear. Some pine apples grown in pots were exhibited, one of which of the Providence variety, was said to weigh 8 1-2 pounds. There were also a great many grapes exhibited in the pots in which they were grown, each specimen having on about six fair sited bunches, well illustrating the convenience and economy of this mode of cultivation.

The vegetables were in the greatest profusion, bat though of the best possible specimens of culture, presented no especial novelty calling for notice in this place.