THE PSILOTALES 



certainly known that all strains are of Japanese 

 origin. For this reason the wild material to be 

 described below is of particular interest. 



Of recognized taxonomic species there are 

 two: P. Jiaccidum Wall., Fig. 230, a rather un- 

 common pendulous form with flattened stems 

 and P. nudum (L.) Beauv. {P. triquetrum Swartz), 

 Fig. 229, with stiff, erect stems, which is much 

 more frequent. To this species Dr HoUoway's 

 prothalli belonged, and since the prothalli 

 were both the starting point and the centre of 

 interest of my personal connexion with the 

 whole group, it will perhaps be appropriate 

 to start with them. 



The sexual generations of the Psilotales have 

 so far only been found in the southern hemis- 

 phere and by very few observers. The first 

 gametophytes of Psilotum were detected near 

 Sydney, Australia, by Darnell Smith and by 

 Lawson, both of whom published notes about 

 them in 191 7, though not all stages required 

 for a complete description of the life history 

 were present. They were apparently not found 

 again until Holloway did so on Rangitoto 

 Island, Auckland, New Zealand, where 

 numerous examples were obtained, many of 

 them bearing young plants, on each of two 

 visits made with an interval of seven years 

 between. These prothalli were the basis of 

 HoUoway's paper of 1938 and of my own paper 

 of 1942. In the meanwhile Holloway had also 

 completed the life history of Tmesipteris by 

 finding prothalli and young plants of this 

 genus also in New Zealand (Holloway, 191 7, 

 192 1 ). By the activities of this one worker the 

 main developmental facts for both genera of 

 the Psilotales have therefore been elucidated, 

 though the cytological interpretation is still 

 somewhat imperfect, as will shortly be seen. 



Fig. 230. Part of a diploid shoot of the pendulous 

 Psilotum Jiaccidum Wall, of unknown wild origin, grown 

 at Kew, from a herbarium specimen. Natural size. 



235 



