THE LEAF. 



227 



In Nymphaea, the apparent fourth sepal in the 

 anterior position has, when compared with that of 

 Nuphar, an anomalous insertion, as it covers the two 

 lateral sepals instead of, as in Nuphar, being enclosed 

 by them. Nymphsea has no bract at the base of the 

 flower-stalk, whereas Nuphar exhibits one. Now 

 Caspar y observed a most interesting abnormality in 

 various species of Nymphsea, viz., the displacement of 

 this apparent fourth sepal into a position at the base 

 of the flower-stalk, showing clearly that it is really 

 the displaced bract, and not a sepal at all, and thus 

 adequately accounting for its covering the lateral sepals. 

 The fourth inner sepal has, owing to this position of 

 the bract, become completely suppressed, and did not 

 even reappear when the bract Avas displaced into its 

 proper position.* In Oarya, both the bract and 

 bracteoles are normally displaced upwards to form 

 part of the calyx. In Loranthus the bract occurs at 

 the top of the flower-stalk, close below the flower. 



Genekal Conclusions on Phyllotaxis. — In the fore- 

 going pages several types of abnormal phyllotaxis 

 have been described. Each of these has its own definite 

 meaning and value whose interpretation has a bearing 

 on the origin of normal leaf-arrangement. 



We must regard the spiral type of phyllotaxis as 

 the primitive one. The floral axis is that part of the 

 plant in which least modification and disturbance has, 

 in the course of evolution, taken place, and is hence the 

 region in which we must look for the most primitive 

 type of leaf -arrangement ; moreover, the sporophyll- 

 bearing axis must always be at least as ancient as, 

 probably more so than, the purely vegetative axis. 



In the more primitive groups of flowering plants 

 the sporophylls are spirally arranged. 



But assuredly the best foundation for the view that 

 the alternate, spiral phyllotaxis is the primitive type is 

 that afforded by the time-honoured p by ton -theory of 



* See Celakovsky's account of this phenomenon. 



