212 ORGANOGRAPHY. BOOK I. 



It is distinguished into three parts ; viz. the radicle (Plate 

 VI. fig. 2. h, &c.) {rhizoma ox rostellum) ; cotyledons (fig. 2. a, 

 Stc), andplumide (or gemmule) (fig. 2. c.) ; from which is also 

 by some distinguished the caulicule or neck [collet, scapus, sca- 

 pellus, or tigelle). Mirbel admits but two principal parts; 

 viz. the cotyledons, and what he calls the hlasteme, which com- 

 prises radicle, plumule, and caulicule. 



Upon certain remarkable differences in the structure of the 

 embryo, modern botanists have divided the whole vegetable 

 kingdom into three great portions, which form the basis of 

 what is called the natural system. These are, 1. Dicotyle- 

 dons; 2. Monocotyledons; and, 3. Acotyledons. In order to 

 miderstand exactly the true nature of the embryo in each of 

 these, it will be requisite first to describe it fully as it exists 

 in dicotyledons, and then to explain its organisation in the 

 two others. 



If a common Dicotyledonous embryo (Plate YI. fig. 2.), 

 that of the apple for example, be examined, it will be found to 

 be an obovate, white, fleshy body, tapering and solid at the 

 lower end, and compressed and deeply divided into two equal 

 opposite portions at the upper end; the lower tapering end 

 is the radicle, and the upper divided end consists of two 

 cotyledons. Within the base of the cotyledons is just visible a 

 minute point, which is the plumule. The imaginary line of 

 division between the radicle and the cotyledons is the cauli- 

 cule. If the embryo be placed in circumstances favourable 

 for germination, the following phenomena occur : the cauli- 

 cule will extend upwards ; the radicle will become elongated 

 downwards, forming a little root ; the cotyledons will elevate 

 themselves above the earth and unfold ; and the plumule will 

 lengthen upwards, and give birth to a stem and leaves. Such 

 is the normal or proper appearance of a dicotyledonous 

 embryo. 



The exceptions to it chiefly consist, 1. in the cohesion of the 

 cotyledons in a single mass, instead of their unfolding; 2. in 

 an increase of their number ; 3. in their occasional absence ; 

 and, 4. in their inequality. A cohesion of the cotyledons takes 

 place in those embryos, which Ga?rtner called pseudomonocoty- 

 ledo7ious, and Richard macrocephalous. In the horse-chestnut, 



