438 OP GENERATION AND DEVELOPMENT. 



thrown at once upon the world, and is dependent for its supply of food 

 upon its own absorbing and assimilating powers ; these enable it to mul- 

 tiply itself by fission, sometimes to a vast extent ; and thus an elaborate 

 and complex organism (such as a Tree-fern) may be produced. In the 

 third form of the generative process, which is peculiar to Phanerogamia 

 (or Flowering Plants), there is the same distinction between "sperm- 

 cells" and " germ-cells ;" but the mode in which the action of the former 

 upon the latter is brought about, is very different. The "sperm-cell," 

 which is known as the pollen-grain, and is developed in the anthers of 

 the flower, does not here evolve self-moving filaments, but, when it falls 

 upon the apex of the style, puts forth long tubes, which insinuate them- 

 selves down between its loosely-connected tissue, until they reach the 

 ovary at its base. Here they meet with the ovules, which are in reality 

 " germ-cells" imbedded in a mass of nutriment stored up by the parent ; 

 and the pollen-tube, entering the micropyle or foramen of the ovule, 

 penetrates into such close approximation to -the germ-cell contained 

 within it, that its contents find a ready passage by endosmose into the 

 latter (Fig. 134, c). Here again, therefore, we have the same essential 

 phenomenon, ^khe intermixture of the contents of the sperm-cell and 

 of the germ-cell, as the condition for the development of the true germ. 

 But this germ, still making its first appearance as a single cell within 

 the ovule, is supplied with nutriment by its parent ; and this not merely 

 whilst the ovule remains in connexion with the organism which 

 evolved it, but for some time subsequently, the store laid up around it 

 in the seed being the material at the expense of which its early deve- 

 lopment takes place. It is not, in fact, until its true leaves have been 

 evolved and its root-fibres have penetrated the soil, which takes place 

 in the act of germination, that it becomes capable of absorbing and 

 assimilating nutriment for itself. As soon, however, as this takes 

 place, the young plant becomes independent of further assistance ; and 

 all its subsequent growth is provided for by its own powers. In pro- 

 cess of time, its generative apparatus is evolved ; and here, too, we find, 

 that the two sets of sexual organs are usually developed in the same 

 organism, it being only a small proportion of Phanerogamia that are 

 dioecious, i. e., that have the male or staminiferous flowers, and the 

 female or pistilline, restricted to different individuals.* 



781. The history of embryonic Development in Flowering Plants, 

 presents some interesting points of correspondence with that of the 

 higher Animals. The germ that is developed within the germ-cell 

 (here designated the " embryonic vesicle" of the ovule) as the product 

 of the admixture of its contents with those of the sperm-cell (or pollen- 

 grain), is itself a single cell ; and the early history of its development 

 closely resembles that which may be observed in all the inferior Plants. 

 In the first place it subdivides into two, each of these into two others, 

 and so on ; its first nisus or tendency being to the production, not of 

 the parts which are to be evolved into the stem, roots, leaves, &c., of the 

 perfect plant, but of a leaf-like expansion, which may be likened to the 



* For a more particular account of the recent discoveries, on which the above ac- 

 count of the Generation of Plants is based, see the Author's " Principles of General 

 and Comparative Physiology," chap, xviii., sect. 2. 



