622 STUDIES IN FOSSIL BOTANY 



in function. It may be added that the very leaf-like 

 character of the bracts in most Sphenophylls, and 

 especially in Sph. majus (p. 1 1 3), makes it difficult to 

 interpret them as sterilised sporangiophores. But 

 whether we regard .S. fertile as a modified or a 

 primitive form, 1 it shows clearly that the sporangio- 

 phores and bracts have equal claims to be regarded as 

 lobes of the sporophyll. This conclusion applies also 

 to Cheirostrobus ; it is only in Sphenophyllum emar- 

 ginatum that the sporangiophores and bracts appear 

 to have been independent, as they have left separate 

 scars on the axis of the cone. 2 



In Calamostacliys, among the Equisetales, the two 

 organs are externally quite separate, but the course of 

 the bundles supplying the sporangiophores suggests 

 that the latter may represent displaced ventral append- 

 ages of the bracts (p. 60). Palaeostachya, from the 

 position of the sporangiophores immediately above the 

 bracts (p. 66), seemed at first to form a link with the 

 Sphenophyllales, but Mr. Hickling's observations on 

 the vascular supply rather suggest a modification of 

 the Calamostachys arrangement. The Equisetum type 

 of strobilus appears to have been already represented 

 in Palaeozoic times, and in Archaeocalamites the bract- 

 whorls were, at most, few and scattered. It has been 

 proposed to derive the bractless arrangement from 

 that found in Sphenophylhcm fertile, the assumption 

 being that the lobes of a wholly fertile sporophyll 

 underwent a displacement like that which appears to 



1 The latter view is maintained by Lady Isabel Browne in her interesting 

 resume of the " Phylogeny and Inter-relationships of the Pteridophyta," 

 New Phytologisl, vol. vii. 1908, p. 94. 



2 As shown by an unpublished observation of Mr. W. Hemingway's. 



