REPRODUCTION IN LOWER PLANT LIFE. 103 
of multiplication is taking place, or is about to take place, 
and in the organs especially connected with it, is not a 
matter of surprise. | 
The close resemblance between a zoospore and an 
antherozoid belonging to one of the lower families of Alge 
has already been pointed out. Both are biflagellate masses 
of protoplasm with a contractile vacuole, and, at least 
usually, a pigment-spot. And there can be no doubt that 
in the zoospore we have the ancestor of both male and 
female elements in the higher plants. A large number of 
the families of Algz produce two kinds of swarm-cell, re- 
sembling one another in every respect except size. The 
larger swarm-cells or megazoospores are purely non-sexual, 
germinating directly into new individuals. The smaller 
swarm-cells, microzoospores, or more correctly zoogametes, 
have but very little independent power of germination ; 
before they can develop into new individuals, two of them 
must coalesce; and this process of conjugation or the 
union of two equivalent or nearly equivalent cells, 
whether motile, asin the case of zoogametes, or stationary, 
as in the conjugation of Sprogyra or the desmids, is 
universally regarded as the lowest phase of a truly sexual 
process of reproduction. 
Let us now examine the phenomena of multiplication in 
the three lowest classes of true Algw, the Ccoenobier 
(including Volvocineew, Hydrodictyerx, Pediastrez, Pan- 
dorinex, and Sorastree), the Multinucleate (embracing 
Siphonez, Botrydiacee, Dasycladacee, and Siphonocla- 
dace), and the Confervoidee Isogamz (comprising Con- 
fervacez, Pithophoraceew, Ulotrichacee, and Trente- 
pohliacez). In most of the genera of these orders we have 
two modes of multiplication, non-sexual by zoospores, and 
sexual by zoogametes. The sexual and non-sexual propa- 
gating elements are alike naked flagellate swarm-cells, with 
