i9*>] DUPLER—TAXUS CANADENSIS 511 



as an outgrowth of the axis, discoid in nature, a view also held of 

 the ovuliferous scale of other forms. Bertrand (3) and Schumann 

 (31) both held the aril to be a special structure, the former regarding 

 it as a proliferation of the cortical parenchyma at the base of the 

 integument (which he regarded as the equivalent of the ovuliferous 

 scale). Jager (15) regards the aril as a second or outer integument, 

 basing his argument on the similarity in origin of the integument 

 and the aril. 



It will thus be seen that the structure is one which has given 

 considerable difficulty in its interpretation, some of the explana- 

 tions being perhaps more ingenious than reasonable. The carpel- 

 lary nature of the aril no longer held sway after the acceptance of 

 the gymnospermy of Taxus. That the aril may be a special 

 structure arising from the axis and having no morphological sig- 

 nificance seems an unnecessary way of avoiding the problem, and 

 while possible is hardly probable. The view which regards it as 

 equivalent to the ovuliferous scale of other forms has more in its 



1 



favor, the chief objections to the idea for Taxus being the cauline 

 origin of the ovule, independent of any recognizable sporophyll, 

 and the belated appearance of the structure. It is hardly reason- 

 able for the ovule to be present for so long and to reach such an 

 advanced stage in development before the appearance of the struc- 

 ture on which it is supposed to be produced. Accepting the aril 

 of Taxus and the fleshy layer of Torreya and Cephalotaxus as 

 homologous structures, there is involved the difficulty of explaining 

 why the aril should be free in one form and organically attached in 

 the others, if representing the ovuliferous scale in all. The entire 

 absence of a vascular supply in the aril of Taxus, excepting the 

 strands which pass through its basal portion, makes impossible an 

 interpretation based on its vascular features. 



The question of two integuments or one seems to be partly a 

 matter of terminology. Distinction needs to be made between 

 the idea of two integuments, an inner and an outer one, and the 

 idea of a single integument of three layers, the outer fleshy one 

 of which may be more or less free from the other two. Coulter 

 and Land (10) have described the situation in Torreya taxifolia, 

 and speak of the outer fleshy layer of the ovule as the outer integu- 

 ment. Concerning Torreya, Coulter and Chamberlain (9) state 



