ANATOMY 421 
particular it is found in Lepidostrobus Brownit, where also the leaf-trace 
bundles are of the mesarch type. The comparison has also been made 
by Miss Ford with Bothrodendron mundum: in this case the corre- 
spondence seems to be rather with the rhizome of Ps?lotum 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! has described the structure of one which may with a 
reasonable degree of probability be referred to Pszlotum. It was 
closely associated with a plant of APszotum, 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 Psz/otum. It was a prothallus of the wholly 
saprophytic, subterranean type, corresponding to that of Z. clavatum 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 sz/otum 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 
14nn. of Bot., xviii., 1904, p. 571. 
