V 
IOWA .ACADEMY -OF SCIENCE 153 
the significant fact in the present consideration is that the more nearly 
central the flower, the farther it is., removed from the main vascular 
supply. 
THE ST AMIN ATE FLtOWER. , t 
The four microsporangia of each stamens are about equal in size’ at 
an. early stage, but later the outer become somewhat larger. This may 
be a mechanical adaptation, since the space available for growth is 
restricted by the tubular coralla. The Stamens enlarge until they touch 
and the .walls ■ of ad j acent stamens unite > by thie ' fusion of contiguous 
eutinized layers (tig. 0); It 1 is possible by considerable pressure to 
separate the anthers of Iva. However the fused layers were in no case 
found to separate, although the cutinized layers sometimes broke loose 
from the epidermis. Tschircli ( 12 ) s holds that j the anthers of the Oom- 
positae . remain - permanently grown together, ‘Mauernd verwacksen 
bleibt,” sinee he was unable to separate them either mechanically or: by 
treatment with, chemical reagents. Britton (1) has taken the Ambrosia 
tribe out of the . Compositae on. the ground that their anthers are ‘‘not 
truly , syngenesious. ? ’ ,It . seems that typical iG'Ohipositae are not alike in 
tips respect, as Is. shown by BtadleWs (12) study of Gnicus in which the 
walls of adjacent inner microsporangia never fuse. It therefore seems 
probable that Gray; (6) is fully warranted in including Iva among the 
Compositae. .smut irfiioq cfil ’> 
The first su gestion : of dehiscence is found in the breaking of the walls 
between the inner and outer microspOrangia;. Schneider (11) has sug- 
gested that’ this -may be due to a growth of the pollen. In Iva the pollen 
grains do enlarge just before m a tur ity an d th is pr ob ably cbntr ibut es ' to 
the rupturing of the walls. 
The lateral pollen sacs of adjacent stamens break together, through 
the dissolution of the' central * portion of the lateral wall, of each stamen. 
In this way five 1 large pollen> chambers are formed, in the fiower^' each ; 
enveloped by an intact wall and : containing the p ollen grains of folih 
microsporangia,— -the lateral pair of each of the tWo contigtions stamens 
(fig. 5). 
Five very small structures, haying t lie appearance of nectaries^ stand 
about. the base of the pistil and alternate with the filaments (fig. 4). 
Martin (8) interprets similar structures in Aster and Solidago as “im- 
perfectly formed stamens.” Goebel (o) has presented evidence that 
certain nectaries arise by the transformation of various morphological 
structures. Merrell (8) suggests that, “It is much more reasonable to 
regard thie* meetary as ah organ of independent Otigin.” Of course 1 it 
