VIl] NEMATOPHYCUS. 197 



and this change in size gives rise to the appearance of con- 

 centric lines indicating periodic changes in growth. 



The radial spaces are characterised by the partial absence of 

 the larger tubes, and as seen in longitudinal sections these spaces 

 constitute regions in which the smaller tubes branch very freely. 

 Fig. 39, B, represents a small piece of a transverse section seen 

 under a fairly high power. In fig. 39, C, the tubes are seen in 

 longitudinal section. The larger elements are unseptate and 

 not very regular in their vertical course through the stem ; the 

 smaller elements are seen as fine tubes lying between and across 

 the larger tubes. In the sections I have examined no un- 

 doubted transverse septa were detected in any of the tubular 

 elements. 



The question as to the possible connection between the 

 larger and smaller elements is one which is not as yet satisfac- 

 torily disposed of. Penhallow' regards the finer hyphal elements 

 as branches of the larger tubes, but Barber^, who has carefully 

 examined good material of Nematophycus Logani, was unable to 

 detect any organic connection between the two. My own 

 observations are in accord with those of Barber. Further 

 details and numerous figures of this species of Nematophycus 

 will be found in the memoirs of Carruthers, Penhallow and 

 Barber. 



Some specimens of silicified Nematophycus stems afford par- 

 ticularly instructive examples of the state, of preservation or 

 method of mineralisation as a source of error in histological 

 work. The sketches reproduced in fig. 39, D and E, were made 

 from a section of a large specimen of Nematophycus in the 

 British Museum. In fig. D we have one of the radial spaces 

 containing some indistinct small elements, the tissue sur- 

 rounding the space appears to consist of polygonal cells 

 suggesting ordinary parenchymatous tissue. In fig. E a few of 

 these ' cells ' are seen more clearly, they have black and ragged 

 walls, and often contain very small and faint circles of which 

 the precise nature is uncertain. The true interpretation of 



1 PenhaUow (89) and (96) p. 46. = Barber (92) p. 336. 



