317 



what obscured by the yellow brown colour of the cuticular 

 substance. 



In this respects the cuticles agrée with those of existing 

 plants, so that the supposition seems justified that the cuticle 

 of Psilophyton was composed of cuticular substances of the 

 same nature as in existing plants. If it be true, that this 

 fossil belongs to the Devonian, of which I hâve no doubt, 

 this is as far as I know the oldest occurence of cuticular 

 substance. (Potonié 1920, p. 185). 



When the material had been in the bleaching liquid for 

 24 hours a small pièce of it drew my attention by its 

 brighter colour, while the other parts were still darkly 

 coloured. Under the microscope it appeared to consist of 

 an aggregate of spores held together by interwoven mycélium 

 threads. In glycérine by slightly pressing on the cover glass 

 the spores could be separated from each others. Most of 

 them were globular, some of them elongated or elliptical, 

 sometimes adhering to each other, forming a short chain. 



The diameter of thèse spores was about 30 — 40 (j- their 

 wall thin, the content brown, with some long crystals, 

 often aggregated, suggesting a nucleus. Some of the cells 

 were burst so that the dark content had disappeared ; the wall 

 now was seen to be without colour. The mycélium threads 

 were colourless also and very thin-walled ; they were 

 repeatedly forked without any transverse walls. 



If we compare thèse features with those known in Rhynia, 

 it is évident that similar characteristics are présent in the 

 latter also. The occurence of a central vascular strand has 

 already been discussed by previous authors. The dimensions 

 of the cells are nearly of the same order ; in Rhynia 

 Gwynne-Vaughani e,g. they are about 50 // broad (K i d s t o n 

 and Lan g 1917, fîg. 32) as in Psilophyton; the length 

 varies. In fig. 31 the cells hâve a dark spot in the middle : 

 sometimes there is a longitudnal ridge as is the case in 

 Psilophyton. 



