212 BOTANICAL GAZETTE [SEPTEMBER 
non. D. opuntioides and D. gracile usually occur on different 
species of plants, hence the food substances which they absorb are 
probably different in some respects. This difference in the charac- 
ter of food material may have given rise to the difference in the 
development of these two parasites. In view of the facts just — 
mentioned, such an interpretation seems quite allowable, since the 
type of reproductive organs formed in Saprolegnia has been shown 
to depend upon the character of the medium in which it is grown. 
Summary and conclusions 
The general plane of branching of Dendrophthora opuntioides 
and D. gracile is isolateral. 
The flower originates a short distance above the axil of the 
subtending bract. 
The floral axis elongates, filling the entire ovarian cavity, and 
does not become attached to the carpels. 
The ovules are greatly reduced, being practically naked nucelli, 
which are borne on a central placenta. There are two nucelli 
oppositely placed in the plane of flattening of the ‘“‘mamelon.” 
In a number of examples vestiges of integuments were found. 
A single archesporial cell, hypodermal in origin, arises in each 
nucellus. The archesporial cell becomes the megaspore mother 
cell, which gives rise to two megaspores. The one toward the apex 
of the ‘‘mamelon”’ gives rise to an embryo sac. 
Following the formation of the 4-nucleate stage of the embryo 
sac, the micropylar end of the sac grows almost straight downward 
until it extends below the level of the insertion of the placenta. 
It then curves outward into the tissue of the carpel, bends, and 
grows upward beneath the lining layer of cells of the ovarian cavity 
until the end of the sac lies almost above the apex of the “ mamelon.” 
The embryo sac is hook-shaped; the short arm of which lies within 
the “‘mamelon,”’ the long arm in the tissue of the carpel. The 
short arms of the embryo sac fuse, forming one continuous tube. 
There are 7 or 8 nuclei in each sac, 2 antipodals in the chalazal 
end of the sac, 3 or 4 in the egg apparatus, and 2 polar nuclei. 
The 2 antipodal nuclei are sister nuclei and were originally the 


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