THE LYCOPODS (CLUBMOSSES) 



it is most unlikely that prothalli would be found at all without the index of juvenile 

 sporophytes to draw the searcher's attention to a suitable spot. 



These facts regarding the discovery of the sexual generation have been given in some 

 detail, partly for their own interest in giving a picture of the genus, but also in relation 

 to the cytological observations on Lycopodium Selago which will be described below. As 

 far as field observations go that species differs in no essential way from the others. 

 Gametophytes are equally rare in all, being 

 apparently produced sporadically in response 

 to locally favourable conditions, and the main 

 colonization of territory is carried out by vegeta- 

 tive growth in the creeping forms, or by bulbils 

 in L. Selago. 



Difficult as it is to grow the prothalli and spores 

 under artificial conditions, the culture of the 

 sporophytes is scarcely less so with the one excep- 

 tion of L. Selago, which will grow readily in pot 

 culture. I have also myself succeeded in keeping 

 L. annotinum alive for several years, but in no case 

 are cones normally produced in culture in the 

 British species. This may suggest that they are 

 not perhaps ideally suited to cytological study, 

 and it may be said without fear of contradiction 

 that for this purpose they are the most awkward 

 genus of Pteridophytes in the whole of the British 

 flora. It is not merely that the appropriate 

 seasons for their study are short and the plants 

 relatively inaccessible, but fixation presents acute 

 difficulties which, added to the extremely peculiar 

 shapes of the chromosomes and other attributes 



which will shortly be mentioned, may make even a successful preparation very difficult 

 to interpret. 



The easiest species to study, however, somewhat surprisingly, and perhaps fortuitously, 

 proved to be L. inundatum. This rather uncommon species was sent to me by post from 

 Aviemore (Scotland), in perfect condition, in July 1936. It had been packed tightly in 

 a tin amongst moist moss, and was still in full meiosis when received. It gave the pre- 

 paration shown in Figs. 243 and 246 a, in which the antenna-like form of the chromo- 

 somes is strikingly displayed. Their number is, however, not in doubt : n = 78. 



The next species to give a result was L. clavatum. This is rather later than most in 

 maturing its spores, and the end of July is more favourable than earlier in the month, 

 both in Scotland and in the Lake District. At the beginning of July, at which season my 

 own material was obtained in the Lake District, meiosis can only be found in the largest 

 cones available, and farther north, in Scotland, this date is definitely too soon. Once 

 material of the right age has been obtained the cytological observations are fairly straight- 

 forward. Fig. 246 fif shows diakinesis sufficiently well spread to enable one to dispense with 



246 



Fig. 242. Lycopodium clavatum L. Young 

 sexually produced plant (right) and a 

 prothallus (left). Natural size. From a 

 photograph kindly supplied by Prof. 

 Lang (cf. Lang, 1899). 



