This section is from the book "The Gardener V1", by William Thomson. Also available from Amazon: The New Organic Grower: A Master's Manual of Tools and Techniques for the Home and Market Gardener.
The fruit is, in the strictest sense of the word, the matured pistil; but Lindley says the term is also applied to the pistil and floral envelopes taken together, whenever they are all united in one uniform mass. The different forms and general characters of the various fruits are very interesting, and are very apt to become stumbling-blocks to many a beginner, as some are so much like seeds, and in some cases seeds are so much like fruits, that at first it is difficult to discern one from another, or, as a Cockney would express it, "t'other from which".
"As the fruit is the maturation of the pistil, it ought to indicate upon its surface some traces of a style; and this is true in all cases, except Cycads and Conifers" (which, as I said on page 226, have their ovules exposed), "which have no ovary. Hence it will be at once seen in the case of grains of corn, and many other bodies that resemble seeds, traces of the style can be seen, so that they are not seeds, but minute fruits." Seeds are almost invariably contained in a seed-vessel called the pericarp, which may consist of the ripened ovary only, or, in the case of the ovary being inferior, of the calyx-tube combined with the ovary. When the pericarp opens, it is said to dehisce; when it neither opens nor splits when ripe, the fruit is termed indehiscent.
All fruits are simple or multiple - a single fruit results from a single flower, or a multiple of fruits from a multiple of flowers. The numerous forms of fruit may be classed among the following, viz. : -
(2) Nut - a dry, bony, indehiscent, one -celled fruit. Ex. Hazel, Acorn.
(5) Capsule - many-celled, dry, dehiscent, syncarpous. Ex. Primrose, Tulip, Violet, Horse-chestnut. There are a great quantity of minor forms that present familiar instances. The following are some of the most familiar, viz.: -
The fruit of the Mulberry may be taken as excellent examples of collective fruit.
Of the many forms of fruit, one of the very curious is the edible portion of the well-known Strawberry; and if the reader will just take one in his hand, he will at once detect little longish spots. These are the true fruit, or, more technically speaking, achenes (aforementioned). The portion eaten is simply a common receptacle for the true fruit. The chief difference between the Strawberry and Blackberry is very apparent, as the carpels of the latter are succulent, and not the receptacle as in the case of the former. The Raspberry is almost identical with the Strawberry.
Many readers of this magazine would no doubt like to see for themselves flowers gradually merging into fruit. If so, let them take particular notice of a certain plant of the common Buttercup (Ranunculus repens) when in full flower, and every day for some time, and they will gradually perceive its slowly approaching fruit; first the petals and then the stamens will go, leaving nothing but the carpels (pistils), which are gradually going into fruit. Each fruit has a peculiar elaboration of its own to perform; for though the fluids afforded by the branches and leaves be nearly similar, yet each fruit differs from another in fragrance and flavour. Six different varieties of the Peach and of the Apple, budded on the same branch, still retain unaltered their times of ripening, and their distinctive colours and flavours. The processes going on at different periods of a fruit's growth are very opposite in their character. During their green and growing state they are usually converting gummy matter into an acid, but during ripening they as commonly are converting an acid into sugar.
To convert gum or mucilage into tartaric acid, as in the early growth of the Grape, oxygen in excess should be absorbed, for their relative components stand thus : -
" Carbon, ....
"They might therefore be expected to absorb more oxygen than the leaves, and this is actually the case; for though a Vine-branch will continue to vegetate in a glass globe hermetically sealed, yet the Grapes upon it will not increase in size unless oxygen gas be from time to time admitted. The same phenomenon occurs during the ripening of the Grapes; oxygen has to be absorbed during the conversion of tartaric acid into sugar, but a larger volume of carbonic acid has to be evolved, and this is coincident with the results of well-established experiments, uniformly testifying that carbonic acid is given out abundantly by ripening fruit".
The forms of fruits we are presented with are innumerable, both in shape, size, and many other characteristics. A very curious one is that of the Pandanus odoratissimus (?), whose fruit, we are told, when ripe, explodes with great violence, and sometimes inflames spontaneously when dispersing its seed. Of our native British plants we have Balsamina noli-me-tangere and Cardamine impatiens, both of which have elastic seed-vessels, which immediately discharge their contents by sudden collapse or recoil of their valves, and the contact of a fly is quite sufficient for this purpose. W. Roberts.
(To be continued).