230 



DE. AGIS-ES AE"BER ON THE 



but the two coneSj which I have described in the preceding section of this paper, under 

 the name of Z. oldhamms f . pilosiis, throw an interesting light on the question. There 

 are no fewer than seven transverse sections of one of these cones (see p. 223), the two 

 uppermost of which pass through the sporophylls above the apex of the axis. The third 

 section (TJ. C. L. Coll., C. 16. c) traverses the tip of the axis. Here we find a vascular 

 cylinder consisting, as seen in transverse section, of a continuous ring of protoxylem 

 elements enclosing a pith, the metaxylem elements being completely absent (Text- 

 iig. 4, A). In this section neither outer nor inner cortex is differentiated, and the 

 sporophyll traces are devoid of the usual sheath of inner cortical tissue. In the next 

 section (Watson Coll., A. 93) there is still no continuous inner cortex, but the outer 

 cortex is differentiated, and there are a few elements of m^etaxylem inside the proto- 

 xylem ring. The sporophyll traces each have an inner cortical sheath, acquired at a 

 lower level. Still further from the apex we come to a section (U. C. L. Coll., C. 16. b) 

 in which the metaxylem is a little stronger (Text-fig. 4, B) and there are traces of tlie 

 inner cortex, while in the next (Watson Coll., A. 94) there is more metaxylem, and the 

 inner cortex is visible as a fragile but approximately continuous zone. The lowest 

 section of all (U. 0. L. Coll., C. 16. a) has the metaxylem slightly better developed 

 (Text-fig. 4, C and PL 27. figs. 50 & 51), while the outer cortex has become fairly massive. 

 It is uncertain how far distant the lowest sections were from the base of the cone, 

 and it is possible that a more complete series would exhibit still further changes. 



Unfo 



b 



of this form figured by Williamson, and the 



of sections f through a cone in the Manchester University Collection resemble the series 

 which we have just discussed in showing only the characters of the apical region of 

 the fructification. 



It is clear that, in the case of Lepidostrolus oldhamius f. pilosus, the radial width of 

 the metaxylem and the degree of differentiation of the cortical layers varied very 

 markedly according to the distance from the apex. This example illustrates the danger 

 of using the anatomical features of isolated sections as diagnostic characters in distin- 

 guishing the species of Lepidostrohus. It is necessary to lay particular stress upon this 

 point, since the attribution of these cones to the Lepidodendroid stems which bore them 

 must depend very largely on anatomical evidence, for lack of petrified specimens shovi 

 actual continuity between the vegetative and reproductive o; 



O" 



5 



6. On the Relation between Strtjcttjiie and Function in the 



Cone-genus Lepibostbobus. 



The cones of Lepidostrobus are markedly uniform in the main features of their 

 structure, but there is, at the same time, considerable variation both in size and form. 

 These fructifications range from a few centimetres to about half a metre in length, and 

 there is a degree of diversity in the form of the sporophylls recalling that to which 

 Brougniart % long ago drew attention in the modern genus Lycopodium. 



* Gen. Coll. Brit. Mas. (Xat. Hist.), V. 8871. 



t Manchester Univ. Coll., R. 385 a & 6, E. 386 a & 6, E. 387. 



X Bronguiart, A. ('37), p. 28 & pi. 12. 



