THE ZYGNEMACEEX 
310 
Iii the second, or lateral form, also called the IUujnchonema 
form, conjugation takes place between cells of the same 
filament, and is effected as follows:—At the point of junction 
of two cells—that is, at the septum, a beak-like swelling, or 
bulging out on one side of the cell walls, takes place; this 
forms a passage of communication between two adjacent cells 
round by one end of the septum; by this passage the contents 
of the one cell pass over to the contents of the other and 
coalesce with them in the usual manner, forming a zygospore. 
It not unfrequently happens that both this and the scalariform 
method take place simultaneously in one and the same species. 
I have often met with examples of Spirogyra insignis and Weber i 
having the same threads showing scalariform conjugation in 
part of their length, and lateral in the remainder. A variety 
of this (lateral) form of conjugation is not unfrequent in some 
species of Spirogyra. It consists in two cells, not in immediate 
proximity, each putting forth at right angles to the axis of 
the cell a side protrusion of the cell-wall; these, becoming 
bent, grow towards each other, parallel with the filament, 
and when they meet the consequences already detailed ensue. 
It sometimes happens, however, that the attempt to unite is 
abortive, the cells being too widely removed to permit the 
connection of their outgrowths before the developmental limit 
of these is reached. These cells are consequently doomed to 
single blessedness, but some sort of compensation is provided 
for such cases as we shall presently see. 
In the third, or genuflexuous , form of conjugation, the 
cells here and there of opposing filaments bend towards each 
other in a knee-like manner until they come in contact ; 
absorption of the cell-walls then takes place at the point of 
contact, permitting the passage of the contents of the one 
cell into the other where coajescence takes place in the usual 
manner, the resulting zygospore being formed in a bulged-out 
portion of the cell-wall at one side. It would appear that this 
process is but rarely performed in its entirety, at least in 
Mesocarpus pleurocarpus (= Mougeotia genuflexa). This is a 
most abundant and widely distributed plant, occurring in 
masses in canals, ponds, ditches, and even in the watering- 
troughs for horses; yet, although I have met with it 
profusely in the geniculate condition, I have never seen it 
in true conjugation, or met with its spore. This being so it 
is difficult to account for its abundance and wide distribution. 
I have remarked, however, that the threads of this plant 
have a great tendency to break up into their component cells; 
whether this may, in some obscure manner, compensate for 
the lack of spores seems problematical, as it is opposed to the 
