THE LIFE -HISTORY OF PLANTS. 



307 



seed forms, after the agency of the pollen, and yet 

 the plant is infertile because the embryo plant is 

 not properly developed. Thus, the fruits of Mui>a 

 Cavenclishii, although they ripen under cultivation 

 here, never produce seed. The capsules or seed- 

 pods of Orchids often ripen and produce abundance 

 of seed, but not perfect seed. The fruits (seeds) of 

 Cycas ripen and develop in our stoves, in all respects 

 perfectly, except in the development of the embryo. 

 Hence the mere ripening of the fruit, or even of 

 the seed, though usually consequent upon fertilisa- 

 tion, may occur exceptionally without fertilisation 

 of the embryo having taken place at all. 



THE SEED. 

 While the ovary is ripening into the fruit, the 



Fig. 100.— Seed of Cotton sur- raised net- 



rouuded by hairs. work. 



ovules in their turn are slowly ripening into seeds. 

 The seed varies- greatly in different plants (Figs. ICQ — 

 103), but what gardeners have chiefly to consider Avith 

 regard to it are its coatings, its perisperm, or store 

 of food (see Vol. L, p. 21), and specially its embryo 

 plant, to which all the rest is accessory, and without 

 which the seed is infertile and useless. As the 

 ovule ripens into seed it usually increases in size, 

 its coats undergo various changes in the way of 

 thickenings, formation of outgrowths, hairs, wings, 

 and the like (Figs. 100 — -103), in the development of 

 colour ; the proportion of water, moreover, greatly 

 diminishes, and the accumulation of reserve material, 

 starch, oil, aleurone, either in the seed itself or in 

 the tissues of the embryo, proceeds rapidly. 



"VNTiile, therefore, the conformation of the seed is 

 such as to insure its preservation and its dispersion, 

 its chemical composition is such as to secure to 

 the nascent embryo -w-ithin, the air, the water, the 

 food, requisite for it till it can feed itself. Obtuse, 

 indeed, must be he who is not struck with this daily- 

 enacted miracle of provident protection. 



One more point of interest may be here mentioned 

 — the relative uniformity of chemical composition in 



the seed. The varying comj)Osition of root, stem, 

 leaf or flower, according to the stage of growth, 

 season, climate, or maniu'e, has been either directly 

 alluded to or must have suggested itself to the 

 reader as a necessary consequence of the activity 

 varying alike in intensity and in kind throughout 

 the plant during its growth. But now things are 

 different. "Whatever have been the fluctuations of the 

 past, whatever actions, reactions, and permutations 

 have been carried out, now has come a period of 

 rest, a condition of something like stability. 



A very interesting illustration of this is afforded 

 by the Eothamsted experiments. Among these is 

 a series showing the results of ninety-two analyses 

 of the ash of Wheat-grain, and ninety-two of Wheat- 

 straw, grown in each case under known conditions 



provided with 



small tubercles. Fig.lOl.— Section of Cotton-seed. 



of soil, season, and manuring. The soil has 

 been analysed, the manures also, the climatic 

 features duly recorded and compared ; moreover, 

 these results are not derived from one season's 

 growth only, but from that of a lengthened series 

 of years. The outcome of this A^ast series of experi- 

 ments is recorded in abstract in the Journal of the 

 Chemical Society for August, 1884. The only point 

 we can here refer to is the fact that, in spite of 

 the very widely different character of the manures 

 employed, provided the seed was fairly ripened, 

 there was a marked uniformity in the mineral com- 

 position of the ripe grain, even where there was 

 wide variation in that of the straw, dependent on 

 supply or exhaustion of mineral food. 



These conclusions are in harmony with what is 

 known of the transfer of materials from the leaves 

 to the seed during growth, and with the general 

 results of the chemical analysis of the seed. In 

 plants under natui-al conditions the ultimate aim, 

 if we may so speak, is the formation and dis- 

 persion of perfect seed. To this all the processes 

 of nutrition are introductorv-, to this all the details 

 of fei'tilisation are j)reparatory. 



