MORPHOLOGY 
like pyrenoids, which are often surrounded by a starch jacket. The 
nucleus is swung in the center of the vacuolate cell by strands of cyto- 
plasm that connect the sheath of cytoplasm about the nucleus with the 
peripheral layer of cytoplasm. The cell division is as described for 
the Mesocarpaceae. 
Sexual reproduction. Sexual reproduction is most characteristic 
(figs. 107-110, and fig. 112). Conjugating tubes put out from the cells 
, of adjacent filaments and fuse, until the 
two filaments connected by conjugating 
tubes resemble a ladder. The protoplast 
of one cell passes through the conjugating 
tube into the connected cell, and the two 
protoplasts fuse, forming a large, heavy- 
walled zygospore. The conjugating 
protoplasts in this case differ in behavior, 
one being passive and the other relatively 
active, so that there is apparent a distinc- 
tion of sex, although the two protoplasts 
are similar in appearance. This distinc- 
tion often extends to the filaments, one 
FIGS, in, i I2 . Zygnema: filament emptying all of its protoplasts 
in. cells showing the two radiating . ,, . . 
chloroplasts, between which is the mto the cells of the connected filament; 
nucleus; 112, conjugation, showing in which case the former filament can be 
two zygospores (each with two regarded as male and the latter one as 
nuclei and four chloroplasts) formed , , T 
by 'the fusion of two protoplasts, female ' Jt ls vel T common to see a 
and a third zygospore-like cell not filament, all of whose cells are empty, 
formed by fusion (illustration of connected with another filament, each of 
parthenogenesis). , . . 
whose cells contains a zygospore. On 
the other hand, the same filament may give and receive protoplasts ; 
and in some species conjugating tubes connect adjacent cells of the 
same filament. Occasionally, also, bodies which resemble zygospores 
are found within cells that have established no connections, and so they 
have been formed without fusion, a phenomenon called parthenogenesis 
(fig. 112). Great variations in the establishment of connections for 
conjugation may be found in almost every collection of zygospore- 
forming material. The zygospore is the winter condition of the plant, 
and upon germination gives rise directly to a new filament. 
Conclusions. The body of the Conjugales consists of a single cell or 
a simple filament, and in its vegetative phase is distinguished by large 
