ZYGOSPORES. 
253- 
base and apex. This occurs in a much higher degree in the Zygomycetes, and 
even in the Myxomycetes, which, growing on a substratum, send up their gonidio- 
phores and sporocarps into the air. 
A non-sexual reproduction takes place universally, but in different ways. In 
the Pandorineae, Desmidiese, and Diatomaceae every cell-division may be regarded 
as a vegetative multiplication, since every single cell constitutes an individual; but 
in the Hydrodictyeos and in Ulothrix peculiar zoogonidia are formed, different 
from the ordinary vegetative cells. Propagation by gonidia takes place however 
in the most perfect form in the Zygomycetes, where, before the formation of the 
zygospores, receptacles are produced on long stalks which develope endogon.Jia 
in vesicular swellings, the so-called sporangia, or conidia (stylogonidia) on branched 
stalks. In many Zygomycetes the much-branched cellular filament which forms 
the mycelium may break up under unfavourable vital conditions into a number of 
spherical cells or gonidia, each of which may subsequently reproduce the plant. 
Many Zygosporeae recall the Protophyta in this respect, that they have also con- 
ditions, during their true vegetative period, in which they have the power of motion ; 
this occurs to an especially high degree in the Pandorinece and Myxomycetes, much 
less so in some Conjugatse and Diatomaceae. 
FORMS CONTAINING CHLOROPHYLL. 
A. Conjugation takes place between motile cells (Zoosporece). 
I. The Pandorine^^ consist of cells which are either isolated or united into 
coenobia by gelatinous envelopes ; the coenobia are either spherical, as in Stephano- 
sphcera, ellipsoid, as in Pandorina, or are square plates, as in Gonium. In these states, 
although surrounded by a cell-wall, they have still a power of motion, each cell pos- 
sessing two long cilia which protrude through the cell-wall. The isolated cells of 
Chlamydomonas and Chlamydococcus swim about in this manner like ordinary zoogonidia; 
in the coenobia, on the contrary, the cilia of all the individual cells project through the 
common envelope, and, by their united action, set the whole coenobium in a twisting 
and rolling motion. The course of life of these plants may be illustrated in two 
examples. 
The genus Chlamydomonas consists of isolated zoogonidia which multiply in the 
vegetative state by bi- or quadri-partition. But in the sexual reproduction the zoogonidia 
divide into eight motile daughter-cells each, provided with four cilia, differing from 
one another in size but smaller than the mother- cells. According to Rostafinski these 
cells conjugate in precisely the same way as Pringsheim has described in the case of 
Pandorina {'vide infra) ; the zygospores thus formed come to rest and continue to grow 
for some weeks ; if then dried and again placed in water they divide repeatedly, and 
form resting motionless families of cells identical with the genus Pleurococcus formerly 
placed under Palmellaceae. 
^ Cohn, Ueber Chlamydococcus und Chlamydomofias, Berichte der schles. Ges. 1856. [Ray Soc, 
Bot. and Physiol. Mem, 1852.] — Cohn und Wichura, Ueber Stephanosphcera pluvialis, Nova Acta 
Acad. nat. curios, vol, XXVI. p. i. [Quart. Journ. Micr. Sc. 1858, p. 131 ; Archer, ib,, 1865, 
pp. 1 16-185.] — Pringsheim, Ueber Paarung der Schwärmsporen, Monatsber. der Berliner Akad., Oct. 
1869. [Ann. des Sc. Nat. 1869, vol. XII.]— De Bary, Bot. Zeitg. 1858, p. 73.— Rostafinski, Bol. Zeit. 
i87i,p, 787. 
