THE PSILOTALES 



which the doubled number of rather smaller chromosomes is visible. Since it is profitless 

 to attempt exact enumeration in a tetraploid without having a diploid of the same species 

 for comparison, I have made no further attempts at greater precision. There is, however, 

 a strong suggestion in Fig. 235 of the presence of some multivalents, and Professor 

 Barber informs me that the same may be seen in Australian tetraploids. It is therefore 

 possible that in this particular species we are dealing with an autopolyploid series. 



This is as far as knowledge oi Psilotum can at present be carried, and there is clearly 

 scope for much further work by anyone with direct access to wild material. The same 



4 ^m 



1 





k. 



^■: 



Fig. 236. Meiotic metaphase and anaphase In Psilotumfiaccidum Wall., permanent acetocarmine. x 1 000. 

 a. After Manton (1942), explanatory diagram in Fig. 237. b. Showing traces of spiral structure. 



is also true of Tmesipteris (Fig. 238). This has been available to me only in Botanic 

 Garden material growing on the stem of a tree fern at Glasnevin in Dublin and believed, 

 though not certainly known, to have come from Tasmania. Since Tasmania is now the 

 centre of Professor Barber's activities, who may be expected shortly to unravel the whole 

 situation, description of my results can be brief. Fig. 239a shows a somatic division in 

 a tapetal cell, and Fig. 239^ is a mother cell at the first meiotic division. The number 

 of chromosomes is horrifying, and I do not propose to attempt an exact enumeration. 

 It is sufficient to state (Fig. 240) that the sporophytic number is between 400 and 500, 

 and that the corresponding gametophytic number is somewhat over 200. That this is 

 also a case of polyploidy is known from an earlier description of c. 100 at meiosis by 

 Yeates (1925) and from Professor Barber himself, who has detected (personal com- 

 munication) two chromosome numbers in Australian material, of which 'somewhat over 

 200' is the higher. With this intimation that polyploidy exists in both genera, we may 

 therefore safely leave the matter in Professor Barber's hands. 



Two things may, however, perhaps be added by way of comment. Both Psilotum 

 Haccidum and Tmesipteris display the same type of curious chromosome shape as that 

 already seen in Equisetum and referable to the same cause, namely, a characteristic 



240 



