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RELATIONSHIPS. 



teristic of medullosan and cycadofilicinean forms we now know with certainty. 

 Kidston has but recently found that in the medullosan form Rhabdocarpon the 

 pedicel of a large seed bore pinnules identical with those of the frond Neuropteris 

 heterophylla. And certainly the amount and character of reduction from the most 

 leaf-like of the Cycas carpophylls to the smallest and most reduced of the Zamia 

 sporophylls is virtually as great as a reduction from a hypothetical zamioid form of 

 megasporophyll with one abortive megaspore to the pedicellate monosporous cycade- 

 oidean type. Indeed, the latter may be the lesser hiatus, for here we have to deal 

 mainly with a radial symmetry and further compacting of form in most obvious 



agreement with physiologic 

 requirements. And do we not see 

 in Zamiostrobus examples of the 

 final reduction stages intervening 

 between the two-spore Zamia stage 

 and the one-spore stage? Have 

 not the sporophylls in this fossil 

 lost all trace of a tip, and are not 

 some of them merely pedicels 

 bearing a single erect and termi- 

 nal seed? In Ginkgo there is some 

 further corroborative evidence of 

 such reduction stages, though 

 more obscure. The Ginkgo stalk 

 bears two bilaterally placed ovules, 

 but one of which is ordinarily 

 functional, though both are so 

 occasionally. Now, could it be 

 _. ,,. proven true that the Ginkgo stalk 



rig. 136. x m 



a, Zamiostrobus stenorhachis Nathorst. Ovulate cone with open habit is & bilobate petiole, as Van Tieg- 



ol growth and 1 to 3 seeds to each sporophyll. From the Rhet o( hem thought, and hence with its 



Sweden. ovules a carpellary leaf, this might 



b. Cycadospadix Hennoquei Saporta. Carpellary leaf with seed at- , . , - _ 



, , i rv ,l i i • n ,l c r, 7ii t, , be cited as an example 01 a gym- 



tached. rrom the Lower Lias, both figures Irom Z.eiller, alter ± &J 



Saporta et Marion. It is necessary to regard these sporophylls as llOSpei'lllOUS reduction Stage Ollly 

 equivalent reductions from ancient foliaceous spore-bearing fronds. ^ little further advanced than ill 



Zamia. But most botanists now regard the Ginkgo stalk and its pair of ovules 

 as a shoot, whence its sporophyll is virtually reduced to the erect monosporous 

 cordaitalean and cycadeoidean form. 



It might be said that the Zamia sporophylls with two oppositely borne ovules 

 are truncate carpels, and that forms bearing a terminal ovule correspond in a way 

 to oddly pinnate leaves. But this must be a minor matter, since both truncate and 

 oddly ovulate sporophylls appear to occur in the same cone in Zamiostrobus steno- 

 rachis of Nathorst. Also, whoever studies the gradual excision of first the distal 

 pinnules and then the complete shortening and reduction of the carpellary leaf in 

 passing from Cycas revoluta to Zamia, and notes the ramose and reduced condition 

 of the terminal bundles in the latter as they pass beyond the large ovule-supply 



