ANATOMY 421 



particular it is found in LepidostKolnis Brownii, where also the leaf-trace 

 bundles are of the mesarch type. The comparison has also been made 

 by Miss Ford with Bothrodendron rnundum : in this case the corre- 

 spondence seems to be rather with the rhizome of Psilotum than with 

 its aerial shoot. 



EMBRYOLOGY. 



Of the embryology of the Psilotaceae nothing is at present known. 

 Even the prothallus has not been recognised with certainty, though 

 Dr. Lang 1 has described the structure of one which may with a 

 reasonable degree of probability be referred to Psilotum. It was 

 closely associated with a plant of Psilotum, in a locality where no 

 species of Lycopodium (with which a mistake of identity might occur) 

 were observed growing in the same situation. This, as well as 

 certain comparative reasons, made Lang regard it as probable that his 

 prothallus is really that of Psilotum. It was a prothallus of the wholly 

 saprophytic, subterranean type, corresponding to that of L. downturn or 

 complanatum : it bore antheridia, but no archegonia or embryos. 



The initial embryology of the Psilotaceae is thus a complete blank. 

 It is to be hoped that ultimately this blank may be filled : meanwhile the 

 following remarks may be made as indicating the nature of the problem 

 which the further data may be expected to solve. The relationship of 

 the Psilotaceae to the Lycopods, long recognised on characters of the 

 mature sporophyte, has lately been in a measure discounted by a better 

 knowledge of the Sphenophylleae, though the prothallus provisionally 

 attributed by Lang to Psilotum would appear to point to a strengthening 

 of the former relationship. A connection also with the Equisetales is now 

 more clearly recognised than formerly ; and it will be remembered that in 

 these the axis asserts itself early, while the first leaf-sheath appears 

 relatively late, as a subsidiary appendage. In the sporophyte of the 

 Psilotaceae we see a rootless plant, with branched, leafless rhizome, while 

 the appendages appear first on the aerial shoot. It may be expected that 

 the embryology should show some evidence bearing on the question 

 whether the leafless and rootless condition of the lower parts is primitive 

 or the result of reduction.' If the embryo showed, like that of Lycopodium, 

 cotyledons and a primary root, that would be positive evidence that the 

 rootless and leafless condition seen in more advanced stages of the plant 

 was a result of reduction. If, on the other hand, the embryo developed 

 without appendages directly into the rootless and leafless rhizome, then 

 either of two interpretations would be possible : either that reduction 

 had been effective back to the earliest phases of the individual : or 

 that the sporophyte at first represented that primitive state of an axis 

 without any appendages, which a strobiloid theory contemplates in the far 

 back ancestry : it is significant that some remote approach to this is seen 



1 Ann. of Bot., xviii., 1904, p. 571. 



