Osborn. — Some Observations on the Tttber of Phy l! agios sum. 513 
Zealand species of. Lycopodium? which form protocorms all have short-lived 
prothalli 1 and grow in localities that are subject to summer drought . 2 
In Phylloglossum the prothallus is stated to be of the L. cernuum type , 3 
whilst the climatic conditions under which it grows are also those of a winter 
rainfall and a dry summer period. The gametophyte generation and the 
conditions of growth are thus similar to those of the protocorm-producing 
species of Lycopods. It is not surprising, then, that Phylloglossum should 
produce a protocorm, since this structure appears to be essentially of 
biological importance in the life-history of plants having a short-lived 
prothallus of the L. cernuum type and growing under special climatic con- 
ditions. Many workers have regarded the tuber of Phylloglossum as a 
protocorm, but this is hardly a legitimate use of the term. By comparison 
with species of Lycopodium it will be recognized that it is the cell mass 
formed by regenerating leaves, and not the tuber which may arise from it, 
that must be considered as the protocorm, since it corresponds to the proto- 
corm of Lycopodium spp. in developmental history and in function. 
Unfortunately the embryology of Phylloglossum is as yet imperfectly known, 
but such evidence as we have indicates that a swollen cell mass is formed 
before the initiation of the tuber . 4 Miss Sampson has recently described 
a sporeling of Phylloglossum, and from her account 5 it is obvious that there 
is both ‘ an embryonic swelling’ and a tuber. Unfortunately the account 
was limited to a single specimen, and it could not be determined whether the 
embryonic swelling was epibasal in origin, corresponding with the proto- 
corm of L. cernuum. This seems probable, and there can be little doubt 
that biologically it is similar, functioning as a primary storage structure. 
In the tuber of Phylloglossum we have a different structure. It has 
repeatedly been emphasized that, in the process of vegetative reproduction, 
tuber and cell mass or protocorm are two structures, the former arising from 
the latter only if conditions be favourable for continued growth. Such 
meagre facts as we have of the embryology are capable of a similar inter- 
pretation. The tuber is something extra, a structure in which Phylloglossum 
has ‘bettered’ the mode of life of certain species of Lycopods 6 (e.g. 
L. inundatum , which annually dies off to the tip of its shoot), since a 
definite tuber is unknown in that genus. Borrowing a term from another 
branch of biological science, the tuber may be regarded as a character of 
considerable ‘ survival value ’, for the climatic and edaphic conditions under 
which Phylloglossum has been studied are severe ; but it seems hardly 
legitimate to style the tuber of Phylloglossum a * protocorm ’ if any morpho- 
logical value is to be retained for that term. That there is a distinction 
between these two organs is borne out to some extent by their differing 
1 Holloway, J. E. ( 1915 ): loc. cit., p. 276. 2 Loc. cit., p. 263. 
•° Thomas, A. P. W. : loc. cit., p. 289. 4 Thomas, A. P. W. : loc. cit., p. 288. 
6 Sampson, K. : loc. cit., p. 607. c Bower, F. O. ( 1914 ) : loc. cit., p. 565. 
