1904] DAVIS—SEXUAL ORGANS IN PLANTS 249 
mother-cells and the amount of sterile tissue developed. These 
tendencies are plainly shown in comparisons of the sexual organs of 
the pteridophytes with those of the bryophytes. The antheridia of 
the former group are all very much smaller than those of the latter; 
the wall of the capsule contains relatively few cells and the amount 
of spermatogenous tissue is very much reduced. Thus where thou- 
sands of sperms are developed in each antheridium of the bryophytes, 
there are less than a hundred formed in most of the pteridophytes, and 
sometimes very few (four in Isoetes). The archegonia of the pteri- 
dophytes have a smaller number of cells than those of the bryophytes. 
The neck region is much shortened and the number of canal cells 
becomes reduced from a large number in the bryophytes to two or 
three in some pteridophytes. Physiologically this reduction in the 
number of gametes, together with the greater specialization of egg 
and sperm, follows a history generally parallel with that in the thallo- 
phytes, and is what should be expected in any series of plants subject 
‘0 the conditions that lead to the high levels of sexual evolution. 
The history of the antheridium and archegonium in the reduced 
gametophytes of seed-bearing plants is not well understood, but 
this is not the time to discuss such difficult and highly special problems 
as the homologies of the stalk and body cell of the pollen grain or the 
88 apparatus and antipodals of the embryo sac. It is certain from 
the transitional conditions presented in the gymnosperms that the 
‘perm and egg nuclei of the spermatophytes are homologous with the 
same samete nuclei of the pteridophytes, and that they stand for 
_ and archegonia which have lost most and in some cases all 
: ‘ € sterile tissue characteristic of these organs as found in the 
"yophytes and pteridophytes. 
— to the origin of the antheridium and fy ssi 
vf a. of Hotrerty are strongly in support of the hypot 33 
iMey be b s'Y Suggested by the author (DAvis’03¢). This a 
archego pniefly summarized as follows: Since the antheridium an 
eee. are multicellular structures from the beginning, and ai 
they ig units developing from well-defined ppt Be 
organs, ( ot have been derived directly from the unicellular yee 
mast ) generally present in the thallophytes. z ey 
arisen from a multicellular structure (gametangium), 
