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 : 



\ Trrt 



FIG. 62. 



A, longitudinal section of one loculus of a young stamen of Euckaridiuin concinuum, 

 showing differentiation of the potential archesporium into fertile cells (a) and sterile 

 cells (s). , similar section of stamen of Clarkia elegans, more advanced, showing a 

 sterile septum dividing the contents of the single loculus into distinct sporogenous groups 

 (i/). * = 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. 



(^) 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 



