452 ME. W. C. WOKSDELL ON THE COMPARATIVE 



minor points, the most essential characters being common to the two genera. This fact,, 

 taken together with the intimate agreement of the two in their vegetative structure, 

 seems to me to be strongly in favour of the future union of these two genera into a 

 single one by systematists. 



I may here remark that the Cycadacese afford a striking instance of a case where the 

 anatomy, even more in some instances than the reproductive parts, may afford an 

 important basis for classification, not only with regard to the different genera amongst 

 themselves, but with regard also to living plants of other groups, and especially to fossil 

 forms. 



2. The occurrence in three of the species examined of more than one vascular ring, as 

 is the case in Cycas and Macrozamia. My specimen of one of these species is a plant 

 many years of age ; the others are adventitious branches of very old plants ; all possess 

 adventitious roots only. 



3. The fourth species [E. horridus, Lehm.), a seedling plant still retaining its primary 

 tap-root, exhibits as yet but a single vascular ring. But in the transitional region 

 between stem and root occur a single large cauline strand and several smaller ones, such 

 as have been described in the main part of the paper above. With regard to these 

 vascular strands I would here adduce the following considerations : — 



a. The plant exhibiting this structure, with its primary tap-root still retained, must 

 necessarily be at a much younger stage of development than any of the other three 

 species. 



h. This being so, it is quite natural to find the outer vascular rings as yet undeveloped. 

 But I hold that the large vascular strand cs^ and the much smaller ones cs^ of fig. 10 

 represent the first sporadic and local beginnings of the second and third vascular rings 

 respectively. At a later stage of growth cambial divisions would extend all round and 

 give rise to the second and third rings in their entirety. 



c. 1 have stated that the small inverted tertiary strands of Jlacrozamia Fraseri, Miq.,. 

 ar(; absent or indistinguishable in Encephalartos caffei\ Lehm. This is true. But in 

 E. horridus, Lehm., there exist strands with inverted orientation, of which cs'^, fig. 10, 

 is an example. This small isolated bundle I regard as a representative of part of the 

 fourth vascular ring and perfectly homologous with the inverted strands belonging to 

 the vascular rings in Macrozamia Fraseri, Miq. 



4. The large, irregularly-shaped, reticulately -thickened tracheides occur, as in Macro- 

 zamia and Cycas, between the xylem of an outer and the phloem of the next inner 

 vascular ring. They are the first-formed, probably secondary tracheides of the former, 

 and may be considered as homologous with the reticulate tracheides occupying the 

 central region of the cortical concentric strands of the stem and root of Cycas. I may 

 here add, with regard to these elements, some observations on the first origin of the 

 vascular tissues outside the central cylinder or stele, as noticed in a young stem of 

 Cycas revoluta, Thunb., where the second vascular ring was making its earliest appear- 

 ance, and in the upper hypocotyledonary portion of the primary tap-root of a seedling of 

 the same plant, where one of the small concentric strands was becoming differentiated 

 imraeaiately outside the central stele. In both these cases it was observed that the first- 



