THE EMBRYO. 



327 



(Fig. 131) and Triglochin (Fig. 626). In the latter, however, close 

 inspection reveals a vertical slit or chink just above the radicular 

 extremity, through which the plumule is j^rotruded in germination. 

 If the embryo be divided parallel Avith this slit, the plumule is 

 brought into view ; as in Fig. 627. If a horizontal section be made 

 at this point (as in Fig. 628), the cotyledon is found to be wrapped 

 around the enclosed plumule, sheathing it, much as the bud and the 

 younger parts of the stem are sheathed by the bases of the leaves 

 in most monocotyledonous plants. The plumule is more manifest 

 in Grasses, especially in the cereal grains, and more complex, ex- 

 hibiting the rudiments of several concentric leaves, or of a strong 

 'bud, previous to germination (Fig. 622-624, and 126-128). In 

 many cases, however, no distinction of parts is apparent until ger- 

 mination commences ; as in the Onion, Iris (Fig. 131), &c. 



644. In several Dicotyledonous plants one cotyledon is smaller 

 than the other, viz. the inner one, when the embryo is coiled or 

 folded. And in all the species of 



Abronia this cotyledon is wanting, 

 so that the embryo becomes tech- 

 nically monocotyledonous. In 

 the Dodder, a genus of leafless 

 parasitic jjlants of the Convolvu- 

 lus family, the embryo also is 

 entirely destitute of cotyledons 

 (Fig. 148). Here these organs 

 are suppressed in an embryo of 

 considerable size ; but in most 

 such parasites, the embryo is very 

 minute, as well as reduced to the 

 greatest degree of simplicity, and 

 seems to remain until germination 

 in a very rudimentary state. 



645. Sometimes the two cotyle- 

 dons of a dicotyledonous embryo 

 are consolidated, or more or less 

 coherent by their contiguous faces 

 into one mass, when they are said to be conferruminate, as in the 

 Horsechestnut, Buckeye (Fig. 629, 630), and the Chestnut. In 

 these, as in other embryos with very thick cotyledons, the Litter are 



FIG. 629. Section of the seed of a Buckeye. 630. A Buckeye in germination. 



633 



