MIDLAND NATURALIST. 83 
D 
tact when cells at the ends of the respective filaments show the 
phenomenon, the union is effected usually in different geometric 
planes as well. No protuberance is formed as is the case in the 
process of conjugation, and as far as I have been able to ascertain 
the contents of the cells in contact of the different filaments never 
fuse, or form any opening whereby the contents could pass through 
from one cell to another. The contact of the cells seems all that - 
results, and the walls of the cells at the angular point of union 
are not perforated, but simply become fastened or glued together 
over an area which does not exceed the diameter of the cells. 
In conjugation of Mougeotia scalaris between different filaments, 
protuberances are formed that gradually approximate, and finally 
on contact open, and the two gametes combine with the formation 
of the zygospore half way between the filaments. There is no stage 
in the process of conjugation of this plant that in any way resembles 
in the least the formation of ‘‘ knee joints." Zygospore and ''knee- 
joints" I have never seen in the same material so that it may be 
concluded in a way that they do not occur at the same time, and 
are therefore entirely distinct life phases that have an entirely distinct 
bearing on the life functions of the plant. As I have never seen 
typically conjugating material with '' knee joints’’ so I have never 
‘seen ee joints’’ in any except in typically vegetative stages, 
and not even when there was a single zygospore present. I have 
made a great many examinations of vegetative and conjugating 
Mougeotia and the conclusions seem fairly conclusive to me. 
The question has often come up to me in the past few 
years: ‘‘What is the biological meaning of the ''knee joints?" 
I have often sought for a favorable occasion to study the 
problem, and at last a chance presented itself when I found 
an abundance of Mougeotia in one of the jars in the labora- 
tory. The material was as healthy, and typical as I have ever 
seen in the field, and was exclusively in the vegetation condition. 
At first very few plants were present, and in a few days nu 
ical examination revealed the presence of the ''knee joints." A 
considerable time was spent in studying the nature of the union. 
It was noticed that in a number of cases of the phenomenon, 
and apparent degeneration, or darkening in color, of the platelike 
chromatophore of one or both of the cells was noticed at which the 
filaments combined. I had about decided after a number of con- ` 
tinued investigations to give up the problem, when by accident a 
