PALAEOZOIC CONE-GENUS LEPIDOSTEOBUS. 227 



from the epidermis of both dorsal and yentral surfaces of the young laminse, and 

 formed a tangled mass filling the spaces between the sporophylls. They are of con- 

 siderable size, varying in diameter from 0'014 to 0*025 mm. Their length cannot be 

 estimated, as they are so much curved and twisted that any section cuts them into 

 numerous segments, but since no septa can be detected, it is probable that they were 

 unicellular. These hairs appear to have been most abundant in the basal region of the 

 laminse. They were ephemeral structures, disappearing in the case of the older sporo- 

 phylls ; those growing from the lateral margins were retained longest. The hairs are 

 so noticeable a feature that I propose, on their account, to distinguish these cones as 

 Lepidostrobus oldhamius^ Will., f. pilosus. 



The sporophylls of L. oldhamius f. pilosus throw considerable light upon the origin 

 of the periderm, which, as I have shown on p. 211, commonly occurs in the 

 cone scales of this genus. In this counection one of the sections f of Cone B in the 

 Manchester University Collection is particularly valuable, since it traverses the apex 

 of the cone above the tip of the axis, and provides a series of transverse sections 

 of sporophylls. Those in the centre are quite young, but in passing towards the' 

 periphery of the section, we meet with progressively older examples. The younger 

 sporophylls are bounded, both dorsally and ventrally, by a very distinct and regular 

 epidermis. In the older sporophylls, on the other hand, the dorsal surface is protected 

 by a layer of periderm. A comparison of such stages as those represented in Text- 

 fig. 3, A & B, renders it highly probable that the phellogen was hypodermal in origin. 

 This suggestion is confirmed by an examination of Cone A. Here, in a transverse 

 section % which passes through the base of a sporophyll lamina at the level of the ligule, 

 we meet with an appearance (Text-fig. 3, e) which exactly suggests, at first sight, an 

 early stage in the development of hypodermal periderm in various modern plants. It is 

 possible, however, that the diagrammatic character of this section may be a little 

 deceptive, and that the apparent tangential strip of *' phellogen " may be due merely to 

 the separation of the cell- walls, owing to splitting during or before petrifaction. But 

 even if this is so, the crack probably followed the plane of weakness of the earliest walls 

 Avhich were laid down when periderm formation was initiated. As an example, from 

 the Phanerogams, of a similar formation of cork for the protection of the reproductive 

 organs, we may take the hypodermal periderm, which is developed in the sepals of the 

 Scrophulariaceous tree, Faulownia imperialism Sieb. & Zucc, even before the flower-buds 

 begin to unfold (Text- fig. 3, B). 



(6) The Ligule. 



In one of the transverse sections 5 cut near the cone apex six ligules are visible 

 {Ig., PL 27. fig. 54). The immaturity of this region of the cone no doubt accounts for 

 the preservation of so large a number of these a 



^T-^ 



• 



These hairs may be compared with those occurring at the base of the sporophyll pedicel in Z. Brownli. 



ZeiUer, R, ('H), pi. 13. figs. 7-9. 



t Manchester Uniyersity Coll., E. 387. 



% U. C. L. Coll., C. 16.a. 



§ Manchester Universitv Coll.. R. 386. 



drawing 



