618 BLACK: BRANCHED CELLS IN THE 
of the retention of the filamentous form of gametophyte due to 
feeble light and poor nutritive conditions and even of a reversion 
to the formation of cell threads, after an expanded prothallium 
had been established when nutritive conditions became unfavorable 
are given in Goebel’s Organography (6, pp. 202-205). 
Some very irregular filamentous prothallia, evidently the result 
of feeble light and poor nutritive conditions, were found by the 
writer in an old culture of Onoclea sensibilis L. A rather unusual 
character of these prothallia was the tendency of certain cells to 
branch. It was thought that a description of them might be of 
interest to others investigating fern prothallia. 
Spores of Onoclea sensibilis were sown upon sterile distilled 
water for class use. Through oversight, the covered glass dish 
containing the culture was left undisturbed in somewhat dim 
light for approximately six weeks. When it was then observed 
the culture appeared green and healthy. Upon examining the 
culture, part of the prothallia were floating on the surface of the 
water and some smaller clumps were entirely submerged near the 
bottom of the dish. Slides were prepared from both sources. 
The prothallia taken from the surface presented the typical form 
with a well-defined apical region as shown in Fic. 1. Some of 
them consisted of thirty to fifty cells and bore a few antheridia. 
The submerged prothallia were found to differ considerably 
from the normal gametophyte. In these prothallia the cells were 
greatly elongated and contained few chloroplasts scattered 
throughout. It was of interest to note that many cells had pro- 
duced one or more outgrowths without cutting off the usual cross 
wall. Fic. 2 shows a five-celled prothallium, the last two cells of 
which are unusually long. The enlarged end of the apical cell is 
turned, indicating an abrupt change in the direction of growth. 
In Fic. 3 a small cell arises from the elongated apical cell. This 
cell is so turned that it is growing in the opposite direction from 
the main apical cell. This cells resembles a rhizoid except for 
its size and the presence of chlorophyll. In Fic. 4, the end of the 
filament forms an acute angle with the main cell-thread. This is 
due to a change in the direction of growth of the apical cell. A 
very small outgrowth is cut off laterally from the apical cell. 
The abrupt turning of the branches is not caused by contact with 
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