THEORY OF THE PROTOCORM. 225 
sporophyte on the soil. Such a suggestion certainly accords readily with 
thé sporadic occurrence of the “ protocorm.” 
"It is difficult to arrive at a conclusive balance between such conflicting 
facts and arguments as these. So far as any conclusion commends itself 
to. my mind it is as follows: A “protocorm” development may have 
been an important phase in the establishment of certain Lycopod embryos, . 
in that’ it serves as a temporary substitute for a root-system delayed ‘in 
its development. But it seems unnecessary to take such cases as proto- 
types for even the genus ZLycogodium as a whole: since the Lycopod 
embryo, while showing essential unity in its general plan, seems prone 
to parenchymatous swelling. Two such swellings, somewhat similar in 
structure but differing in place of origin and in function, are known, viz., 
the enlarged “foot” of Z. clavatum and annotinum, which originates 
from the lower tier of cells of the embryo, and is intra-prothallial ; and 
the “protocorm” of the cernwm-type, which originates from the upper 
tier of the embryo, and is extra-prothallial They are both biologically 
intelligible, for the former acts as an haustorium, the latter may be a 
ready mode of fixation in the soil, and also a specialised place of storage. 
A genus which shows two types of parenchymatous swellings in two 
distinct types of embryo, while both are absent from other species of 
the genus, cannot be expected to have ever had one of these as a 
constant feature in its ancestry. This consideration makes me doubt 
any general application of the theory of the “protocorm” even in the 
genus Lycopodium. These parenchymatous swellings may be looked upon 
as opportunist growths, rather than as persistent relics constant from a 
remote ancestry. This view is greatly strengthened by the occurrence of 
protocorm-like developments in isolated cases among the Angiosperms. 
Phylloglossum with its large storage “protocorm” would then be the 
extreme type of a line of embryological specialisation, not a form pre- 
serving the primitive embryological characters of the whole race. On 
such grounds, while not denying that a “protocorm” may have had a 
certain importance in certain cases, the facts do not appear to justify 
attaching to it any general significance. 
From the above pages it will be plain that the origin of the free- 
living habit of the sporophyte, and of its root-system is quite as obscure 
as that of the leafy shoot itself. The important step from dependent to 
free life was certainly taken at a period before the earliest fossil records of 
Vascular Plants; for all the best-known types of early fossil Pteridophytes 
have roots assigned to them on secure grounds of observation: so 
naturally the evidence from them does not lead to a solution of the 
difficulty. On the basis of comparison, to which this question must 
necessarily be relegated, no decisive help is forthcoming; the theory of 
the protocorm, which at first sight seemed so full of promise, does not 
give more than a suggestion how the transition from dependence to 
independence may actually be carried out in certain cases, and among 
P 
