718 
DUNCAN S. JOHNSON 
per cent of these stamens had the usual complement of four 
sporgangia (figs. 10, 16, 20). About 22 per cent of them had 
three sporogenous masses each (figs. 21, 22, 31). The larger 
proportion, 37i per cent of all the stamens, had only two groups 
of sporogenous cells, which may both be in the same theca 
(figs. 26, 27, 28), or on opposite sides of the connective (figs. 23, 
24, 30). In a very considerable proportion of the stamens but 
a single pollen mass is formed. This was found in 17J per 
cent of those counted. The sole remaining spore mass may be 
on either the acroscopic or the basiscopic side of the connec- 
tive (figs. 27, 28), or it may extend past the connective from 
one theca to the other (figs. 25, 29, 31). In all cases of this sort 
seen, the mass was continuous across the ventral side of the 
stamen (figs. 29, 31). Finally, 10 per cent of the stamens 
counted were devoid of any sporogenous tissue whatever (figs. 
32, 51). 
Not only does the arrangement of the sporogenous tissue differ 
in different stamens, but serial sections show that it differs at 
different levels in the same anther (figs. 22, 23 — fig. 23 being nearer 
the top of the anther). 
Two types of reduction in the number of spore masses can be 
distinguished among the stamens illustrated in figs. 20 to 32. 
There is one series of cases in which each of the masses present is 
in the position of one of the four sporangia of the normal stamen, 
while one or more of the regions usually occupied by a sporangium 
remains entirely sterile (figs. 9, 26, 28). In a second series of 
cases the regions usually occupied by two or three distinct spo- 
rangia, together with the larger or smaller sterile region between 
these, is occupied by a continuous sporogenous mass (figs. 21, 
23-25, 27-31). No stamens were seen in which a continuous 
sporogenous mass seemed to fill the regions occupied by all four 
of the sporangia of the normal stamen. 
The first type of reduction mentioned is evidently an example 
of the phenomenon referred to by Goebel ('05, p. 554) as the ar- 
rest or suppression of pollen sacs," and spoken of by Bower 
('08, p. 127), as the ''abortion of the sporangia." Cases of this 
