PBOBLEMS OF PROPAGATION. 



455 



for use. Placed in the required conditions, it exhibits phenomena 

 fundamentally diverse from those shown by the dicotyl : 



(a) . First of all, nO' callus is formed. Only a skin of cork is 

 produced to cover the wounded surface. 



(b) Then no roots are sent out from the stem of the cutting. 



(c) A bud in the axil of the lowermost leaf on the cutting (or of it 

 and of the one immediately above it) begins to enlarge, and, as it does 

 so, from its base emerge new rootlets. This enlarging bud is the 

 beginning of the new plant that is to come from the cutting. As the 

 bud spreads laterally it sends up aerial shoots, and, as these develop, 

 the portion of mother-shoot used as cutting withers and dies off. It 

 takes no share in the formation of the new plant (figs. 164, 165, 166). 



This distinctive difference in behaviour of dicotyls and monocotyls 

 seems to be no chance one. It belongs, I believe, to phyletic history, 

 and is of the essence of the constitution of the two groups of plants 

 Let me explain. 



DtcotylouLS Morwcoty Lolls 

 seedlings 



Fig. 160. 



The cormic construction of the dicotylous plant shows us : 

 (a) The hypocotyl or body — central axis — of the corm. 

 (5) The primary root in line with, and at the basal end of, the 

 hypocotyl. 



(c) The suckers (cotyledons) two lateral extensions of the upper 

 part of the hypocotylar region of the corm. 



{d) The plumule — which is the primordium of the future aerial 

 extension of the shoot of the plant, and it lies at the apical terminal 

 point of the hypocotylar region. 



Compare now the like parts in the monocotyl — there is : 



(a) The hypocotyl. 



ih) The primary root. 



(c) One sucker (cotyledon), an upward terminal extension of the 

 hypocotylar region. 

 I {d) The plum.ule, which is here a lateral structure on the hypo- 

 \ cotylar region. (Fig. 160.) 



! From the beginning, then, the dicotyl has the instinct of upward 



