to the Plant Cell. 523 
Overton has concluded that lecithin plays an important role in the absorp- 
tive properties of the cell. He thinks that only those substances are 
absorbed which are soluble in the oily or fatty substances such as lecithin 
and cholesterin, which impregnate the cell-wall. Pfefifer remarks in this 
connexion that such impregnation may play an important part in regulating 
absorption, but, at the same time, the proteid constituents of the plasmatic 
membrane are also of importance. Lecithin is soluble to some extent in 
water, and may serve as a vehicle for the assimilation of fats. It is rather 
improbable that the chief function of lecithin is to serve for respiration, 
as Loew suggested. It may be pointed out that those tissues of animals 
which contain relatively large amounts of lecithin are not necessarily active 
agents in respiration. 
Hydrodictyon died within two weeks after being transferred to a 
nutrient solution containing no phosphorus. The cells which died during 
the first few days of the experiment contained considerable starch, but 
where the cells died slowly the pyrenoids and their deposits of starch 
seemed to be consumed. Whether the cells died slowly because they were 
able to make use of the material of which the pyrenoids were composed, 
I was unable to determine. 
When filaments of Spirogyra were cultivated in solutions which lacked 
phosphorus they showed the injurious effects at the end of three weeks. 
At that time many of the cells were dead, and the remainder showed 
evidence of greater or less injury. The contents of the dead cells were 
completely broken down ; the nucleus having broken from its radiating 
strands of protoplasm was usually at the end or upon one of the lateral 
walls of the cell. 
There appeared to be three well-marked stages in the death of 
Spirogyra cells in the solutions lacking phosphorus. In the first stage, 
the cell contents appeared cloudy, and the Marchi test usually showed that 
fats were present. This was undoubtedly due to the fact that the usual 
formation of lecithin was not going on, owing to the absence of phosphorus, 
and in consequence there was an accumulation of fats in the cells. In the 
second stage the chlorophyll bands became disarranged, either by taking 
a position nearly parallel to the long axis of the cell, or by rolling up 
in close spirals. In the third stage all green pigment disappeared from 
the chloroplasts, and the cell contents suffered complete disorganization. 
At the same time the filaments themselves were broken up in a very 
characteristic manner. Some time previous to the death of the filaments 
they had broken up into short rods composed of two or three cells, 
and, in many cases, the individual cells were entirely separated from 
neighbouring cells. The cells in this isolated condition appeared to 
suffer no more injury or to die no sooner than those which retained 
their normal relations, 
P p 2 
