Sir obi his in Archegoniate Plants . 361 
peduncle is the simple strobilus : its conformation does not 
differ very materially from that of Equisetum , beyond the 
smaller number of the sporophylls, and the fact that each 
bears but one sporangium upon its upper surface, instead of 
a number affixed all round. From Phylloglossum the advance 
to the more complex Lycopods can best be understood by 
comparing them in the young state : the similarity of the 
young plant of L. cernuum to that of Phylloglossum is so 
striking that it has been recognized by various writers : the 
chief difference lies in the leafy bud which in Lycopodium 
replaces the strobilus of Phylloglossum , and grows on into 
the Lycopodium plant as we know it. On our hypothesis 
we may understand how continued apical growth of the 
strobilus would lead to its elongation, and increase in number 
of sporophylls, sporangia and spores : branching of the strobilus 
has been seen in Phylloglossum , but is a more prominent factor 
in Lycopodium . Meanwhile, in order doubtless to increase 
the vegetative system necessary for the nutrition of the larger 
number of spores, the lower sporangia would be arrested, the 
subtending sporophylls developing as foliage-leaves. In 
species such as L. Selago alternating sterile and fertile zones 
appeared, in others as L . clavatum the whole lower part of 
the plant is vegetative, while the strobili occupy the ends 
of special branches. It is thus possible to recognize the shoot- 
system of living species of Lycopodium — exclusive of the 
protocorm and protophylls — as the result of continued growth 
and branching of a strobilus, the lower parts of which have 
become sterile. 
Within the genus Lycopodium , but more obviously in Lepido - 
strobus and Isoetes , differences of size of the individual 
sporophylls, and of bulk of the individual sporangia, are 
seen : the latter show very large sporangia as compared with 
Lycopodium , and we may recognize as one of the methods of 
increase of the output of spores, the increase in size of the 
individual sporangium. But with this would come again the 
difficulty of nutrition, and danger of damage. These are 
partially met in Isoetes and Lepidostrobus by processes of 
B b 2 
