OF THE EMBRYO AND SEEDLING. 23 



prolongation of it, that it was called the descending axis ; and 

 the body from which it originates was named the radicle, on the 

 supposition that it was itself the nascent root. But, as already 

 explained, the so-called radicle grows in the manner of stem (24), 

 and is morphologically that initial internode the node of which 

 Dears the first leaves or cotyledons. (20.) Let it now be noted 

 that this descending axis or single primary root is far from 

 universal. In Pumpkin, Squash, Echinocystis, and the like, 

 the strong caulicle sends out directly from its root-end a cluster 

 of roots or rootlets, of equal strength; i. e., it strikes root in 

 nearly the manner that a cutting does. (Fig. 47.) 



38. The Polycotyledonous Embryo is one having a whorl of 

 more than two seed-leaves. The dicotyledonous embryo being 

 a whorl of the very simplest kind, that is, with the 



members reduced to two, the pobycotyledonous 

 may be regarded as a variation of it. In all but 

 one group of plants it is simply a variation, of 

 casual occurrence, or even a monstrosity, in which 

 three or rarely four cotyledons appear instead of 

 two. In Pines (Fig. 48, 49), however, and in 

 most but not all Coniferse, a whorl of from 3 to 10 

 cot}'ledons is the normal structure, varying accord- 

 ing to the species, but of almost uniform number 

 in each. In germination these are brought out of \| 

 the soil by the elongation of the caulicle, and when 

 the husk of the seed is thrown off they expand 

 into a circle of needle-shaped leaves. In the Pine 

 tribe, all the subsequent leaves are alternate (spiral) in arrange- 

 ment, with some disguises. In the Cypress tribe, the cotyledons 

 are fewer (not more than four, and more commonly only two) , 

 and the subsequent leaves also are in whorls of two to four ; 

 i. e., are either opposite or verticillate. From the occasional 

 union at base of the cotyledons of a polycot} T ledonous embryo in 

 pairs or groups, and from a study of their early development, 

 Duchartre 1 plausibly maintains that such cotyledons really consist 

 of a single pair, parted into divisions or lobes. The ordinary- 

 interpretation, however, is equally tenable. 



39. The Monocotyledonous Embryo, although theoretically the 

 simplest, is practically a more difficult study. It has a single 

 cotyledon (as the name denotes) ; also a single leaf to each node 



1 Ann. Soi. Nat. ser. 3, x. 207. This view, which originated with Jussieu, 

 is adopted by Parlatore in DC. Prodr. xvi. 



FIG. 48. Section of a seed of a Pine, witli its embryo of several cotyledons. 49. Early 

 seedling Pine, with its stem let, displaying its six seed-leaves. 



