26 



MORPHOLOGY 



matter furnished by the albumen, and to transmit it to the 

 growing plumule. The plumule consists of a succession of 



rudimentary leaves, sheathing 

 and enclosing one another, on 

 the summit of a very short 

 axis, which is mainly the 

 caulicle, otherwise called rad- 

 icle. This is completely en- 

 closed by a basal portion of 

 the cotyledon and of the 

 outermost leaf of the plu- 

 mule, which form a peculiar 

 sheath for it, named the 

 Coleorhiza? i. e. root-sheath : 

 consequently the first root or 

 roots have to break through 

 this covering.* As in the Oak 

 and Pea(32), the very first or 

 outermost leaves of the plu- 

 mule develop Imperfectly and not into 

 efficient foliage. The one in Fig. 62, 

 which encloses the rest in the early 

 growth, is left behind as a mere sheath 

 to the base of the following and more 

 perfect leaves : it is the same as the 

 lowest in Fig. 63. The leaves are first 

 developed : the internodes lengthen later, and the lowest lengthen 

 very little. Not rarely the first root starts singly from the tip of 

 the caulicle (Fig. 62, just as in Fig. 55) ; but others of equal 

 strength follow from any part of the caulicle, and soon from 

 the nodes above ; and no tap-root is ever formed. 



42. A Pseudo-monocotyledonous embryo occasionally occurs ; 

 that is, one of the dicotyledonous type, of which one cotyledon is 

 wanting through abortion. This occurs in Abronia, a genus 

 related to Mirabilis, and bearing an embryo very similar to that 

 represented in Fig. 17, 18, except that one cotyledon is absent. 

 The anomaly of an acotyledonous embryo occurs in Dodder, a 

 plant of the dicotyledonous type, but with both cotyledons 



1 This, the Coleorhize of Mirbel, should not be confounded (as by some it 

 has been) with the "root-cap," or tissue which ordinary roots (whether 

 primary or secondary) break through in their development or carry on 

 their apex. 



FIG. 62. Early germination of Indian Corn. 63. More advanced germination of 

 same : roots produced from portion of stem above the cotyledon as well as below. 



