250 BOTANICAL GAZETTE foctoser 
which was probably at the level of isogamy in its sexual evolution, 
because the gametogenous tissues in the antheridium and archegonium 
are essentially similar in structure, as is also true of the sterile tissue 
forming the surrounding capsule. The only multicellular reproduc: 
tive organs of the thallophytes which offer any possible points of 
relation seem to be the so-called plurilocular sporangia or game: 
tanga of the Phaeosporeae, and similar structures in certain green 
algae, Schizomeris, Stigeoclonium tenue irregulare, and conditions 
occasionally found in Draparnaldia and Chaetophora. Such multi 
cellular reproductive organs of course must be regarded only a 
representatives of a certain type of structure (sporangium or game 
‘tangium), and not as direct ancestors of the sexual organs of bryo- 
phytes and pteridophytes. I have never associated the archegonium 
closely with any individual form as Miss Lyon (’o4, p. 281) might 
lead one to suppose. 
These sporangia and gametangia of the brown and green algae 
have the peculiarity that the original cells divide up into a great num 
ber of very small cells (loculi), each of which often develops but 3 singe 
zoospore or gamete. It is probable that the extensive cell division 
by which each zoospore or gamete is often given a separate compat 
ment in the general structure is responsible for the origin of a mult 
cellular reproductive organ (sporangium or gametangium) rigs bil 
type of unicellular structure (sporocyst or gametocyst). bane! 
angia and gametangia of the brown and green algae are known 2 
‘modified branches, generally somewhat smaller than vege 
branches. Should such gametangia be placed under environmen 
as from wale? 
conditions demanding protective coverings (as bya change 1™ i 
to a land habitat), the first expression would be the sterilization?” 
outer layer of cells to form a protective capsule around penne 
gametogenous tissue. Such an advance would give the por 
ture of an antheridium and an archegonium, and further spe@ pee 
need be only along the well-known lines of sexual eo dts 
by which one form of gametes would become son through 
small sperms, and the other form, by loss of motility a” erial for @ 
numerical reduction and consequent conservation of mr beet 
few gametes, would become large eggs. These yee 
discussed in full in the author’s paper on “The origin © 
