FACTORS OF INCREASE 121 
have the numerous small loculi arranged in four rows, corresponding in 
position to the four pollen-sacs of the normal anthers in other genera of 
the family, the only essential difference from these being the presence of the 
septa which separate the loculi. The cells which form the septa are similar 
in position to the archesporial cells of the normal anther (Fig. 62), and the 
conclusion is that certain of the archesporial cells are no longer fertile, 
but develop to form the sterile tissue of the septum. A similar argument 
will apply for other families of Angiosperms with varying degrees of 
cogency, according as the septate anthers diverge less or more from the 
usual type, or according to the less or greater isolation of the genera 
which show the multilocular state. In the Pteridophytes also there are 
cases of juxtaposition of loculi similar to those in the septate anthers: 
Fic. 62. 
A, longitudinal section of one loculus of a young stamen of Hucharidium concinuunt, 
showing differentiation of the potential archesporium into fertile cells (a) and sterile 
cells (s). SB, similar section of stamen of Clarkia elegans, more advanced, showing a 
sterile septum dividing the contents of the single loculus into distinct sporogenous groups 
(sf). ¢=tapetum. X 365. 
conspicuous instances are found in the spike of Ophioglossum, and in the 
sorus of Danaea. But the development in the Pteridophytes gives less 
conclusive evidence than in the anthers of Angiosperms, owing to their 
meristems not being stratified, and to the fact that the genera are 
more isolated. But though the facts in these plants do not amount to 
a complete demonstration, there seems a reasonable probability that 
septation has played a part among them also. Whatever view be taken 
for these Pteridophytes, it is clear from the examples quoted from the 
Angiosperms that septation of sporangia previously in the race non-septate 
has been a factor of increase in number of sporangia. 
(4) By the formation of new sporangia, or interpolation, is meant the 
initiation of a new sporangial primordium, or of several, at a spot previously 
in the race not so occupied. The results of this mode of increase may 
in some cases be difficult to differentiate from those of septation, where. 
