340 BOTANICAL GAZETTE [May 
14. The outer wall of the microsporangium is usually four 
layers thick, the innermost layer being part of the tapetum. The 
inner wall, that is the cells between the base of the sporangium 
and the vascular bundle, is probably formed by sterilization of 
cells derived from the primary cells of the sporangium. 
15. The divisions of the microspore mother cells may be 
either successive or simultaneous. The two spindles of the sec- 
ond division do not become connected by secondary fibers. The | 
microspores are usually bilateral but sometimes tetrahedral. 
16. The number of microspores in a sporangium is 150,000- 
300,000. 
17. A sporangium first becomes recognizable as a megaspo- 
rangium by the marked enlargement of many or most of the cells 
of about the third and fourth layers. All such enlarged cells 
are to be regarded as potential mother cells, and the number 
of them which succeed in producing megaspores is probably 
dependent on nutrition. No tabular tapetal cells are cut off in 
connection with the development of the megaspore mother cells, 
nor is the megaspore mother cell the innermost of a row of cells 
formed from a single archesporial cell in a manner comparable to 
what is seenin the ovules of seed-plants. | 
18. Many cells which enlarge almost to the size of mature 
mother cells are finally unable to give rise to spores, but divide © 
up into smaller cells which ultimately form part of the tapetum. 
19. The trabeculz, tapetum, and walls arise in the megaspo- 
rangium as in the microsporangium, the chief difference being 
the greater massiveness of the single trabecule in the former 
and the much greater abundance of the tapetum. 
20. No details of the division of the megaspore mother cell 
were obtainable. The megaspores are usually tetrahedral in 
arrangement, but occasionally bilateral. The number in a Spo- 
rangium is 150-300. 
21. The first leaves of a season are megasporophylls, 
these are succeded by microsporophylls. There is occasionally 
some irregularity in the order of succession, and sometimes 4 
sporangium is found which bears both kinds of spores. 
and 
