CHAPTER 14 

 THE PSILOTALES 



The Psilotales are a microphyllous group without close relatives and without known 

 ancestry. They are microphyllous in the sense that they are certainly not megaphyllous 

 like the ferns, though it is an open question whether in fact they possess leaves at all, the 

 curious little appendages borne on the aerial portions of their stems being so unlike 

 leaves in the ordinary sense that they are perhaps not of this nature. Psilotum and 

 Tmesipteris are the only known genera, each containing only one, or at most two or three 

 species, none of which is native to Europe or nearer to our shores than the tropics and 

 the southern hemisphere. Nevertheless, so important are they in all morphological dis- 

 cussion of the Pteridophyta that they cannot be omitted. In their complete absence of 

 roots and in other relatively simple features they are now generally regarded as in all 

 probabihty the most primitive of living vascular plants, and if any relationship can be 

 established with other members of the Pteridophyta it is Hkely to be with the long- 

 extinct Psilophytales, themselves the simplest vascular plants known to science, rather 

 than with any more recent group. 



Fortunately, though not native to Europe, examples of both genera are available in 

 botanic gardens and, in addition, I was in the uniquely favourable position of having 

 been entrusted in 1939 with the cytological examination of both sporophytes and 

 gametophytes collected in New Zealand by the late Dr HoUoway of the University of 

 Otago and described by him in the Annals of 'Botany of 1938 and 1939. There were 

 special peculiarities about Dr Holloway's prothalli which made a cytological study of 

 them desirable, and the cytological findings were published in detail in 1942 (Manton) 

 to preserve them from risk of loss by enemy action. The observadons recorded in that 

 context are still the most important contribution that I personally have to make to know- 

 ledge of this group, but through the kindness of Professor H. N. Barber of Tasmania, who 

 has communicated privately some additional observations from Austrahan material with 

 permission to quote them, a few additional facts can now be supplied. Since I understand 

 that Professor Barber is also himself engaged on further study of both genera on native 

 Austrahan material, the account to be given below need only be regarded as an interim 

 statement, of value in the present connexion for comparative purposes with the other 

 great groups, and as neither final nor exhaustive in itself. 



Members of the genus Psilotum are found in the tropics right round the globe, though 

 they are familiar objects in most botanic gardens since they are fairly easy to grow and, 

 in addition, reproduce themselves by bulbils wliich are very easily transported. They 

 are therefore Uable to spring up unexpectedly as weeds in tropical glasshouses where pot 

 plants are grown, and may have been repeatedly introduced to Europe along with other 

 plants. This is partly the reason why a place of origin can rarely if ever be assigned to 

 botanic garden material, and even in Japan, the only country in which they appear ever 

 to have been extensively grown for horticultural purposes (Okabe, 1929), it cannot be 



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