142 THEORY OF THE STROBILUS 
sterile central columella: such was probably the case also in the predecessors. 
of the strobilus, but the process was more completely carried out, so that 
the spore-formation came to be, as it now is in all Pteridophytes, located 
close to the outer surface. A further step would be the disintegration 
of the sporogenous tissue into separate pockets or sporangia: of such 
disintegration there is evidence in certain Pteridophytes, but it is exemplified 
in the clearest way in the anthers of various Angiosperms: the condition 
which is actually seen in the anthers of Viscum album, or in the large 
multilocular anthers of Aizophora illustrates the point (Fig. 72): here 
the numerous, small, isolated loculi 
cover the very considerable surface 
of the enlarged stamen, and develop- 
ment as well as comparison points to- 
an origin of these by segregation from 
the normal type of pollen-sacs. The 
outgrowth of appendages by enation, 
from such an apically growing struc- 
ture has been already recognised as a 
probable feature; if this took place 
either between the segregated loculi 
or below them so as to carry them 
outwards beyond the general surface, 
during its acropetal development, the 
result would then be a strobiloid 
SOA Sens 
SRY structure with an acropetal succession 
SES : ‘ f 
f of appendages, such as is seen in 
S various Pteridophytes. Sometimes the 
sporangia might be borne in close 
Fic. 72. * relation to the axis, as in Lycopodium 
Rhizophora mucronata. Flower in longitudinal Ot Selaginella, while other Lycopods 
section. Numerous spherical microsporangia, 9, : i : 
in the anther. (After Goebel.) illustrate varying degrees of the carry- 
ing of the sporangia outwards upon 
the appendage. In other cases varying numbers of sporangia’ are borne 
upon a single appendage, as in the Calamarians and Sphenophylls: and 
according to their form, and their relation to or freedom from sporangia, 
divers ranks of these appendages may be distinguished: these matters will 
be discussed in detail later. 
In the hypothesis thus sketched there are several steps which may be 
named as distinct, though actually they may have overlapped: they are 
(1) the differentiation in the primitive sporophyte of a vegetative base, 
and a fertile upper region having a power of apical growth: (2) the 
relegation of sporogenous cells in the latter to a superficial position : 
(3) the segregation of them into separate pockets or sporangia: (4) the 
enation of the appendages. Every one of these steps has its actual prototype 
among living plants, so that nothing is advanced which is contrary to 
