Nemalion multi fidum, Ag . 331 
he described as penetrated by radiating granular strands, should be con- 
sidered as the pyrenoid. 
Timberlake (1901), working on Hydrodictyon , described its pyrenoid, 
which is protein in nature, as cutting off segments from itself in the form of 
concentric discs, which, by the deposition of starch, become transformed 
into starch grains. 
Lutman (1910) has not been able to confirm Timberlake’s results for 
Closterium . He found that the pyrenoid is not homogeneous, but is cut 
into by radiating clefts of lighter staining capacity. He considered it more 
probable that the cleavage resulting therefrom gives rise to new pyrenoids 
rather than to starch grains. All the starch grains, however, are formed 
around the pyrenoid. 
McAllister (1914) described the chloroplast of Anthoceros as contain- 
ing a large number of very small, distinct, proteid pyrenoid bodies, which 
probably increase in number by fission, the ones near the periphery of the 
chloroplast being transformed directly into starch grains. 
Miss Bourquin (1917) has recently contradicted the earlier workers on 
Zygnema , by describing the formation of starch grains as taking place 
entirely independently of the pyrenoid, the latter apparently exerting no 
influence upon the process. 
It will be seen, therefore, that there has been a wide difference in 
opinion with respect to the method by which the pyrenoid acts. Almost 
all workers are agreed, however, that it exerts some kind of an influence 
upon the development of starch, or, in other words, that it represents 
a photosynthetic centre. 
There is no reason for believing that the pyrenoid of Nemalion is 
merely a mass of reserve food. We invariably find that wherever photo- 
synthesis is most likely to occur, as at the periphery of the thallus, it is 
there that the pyrenoid is of largest size and of greatest prominence. On 
the other hand, all cells which are buried in the thallus, away from the 
more direct light, have a pyrenoid which is much reduced, or sometimes 
entirely wanting. If the central body were a mass of reserve food, it would 
be reasonable to suppose that it would be at least as plentiful in the inner 
as in the outer cells, for the food elaborated in the outer cells must be 
passed inward to all the living cells of the plant. The relative prominence 
of the pyrenoid seems rather to be correlated with photosynthetic activity. 
Besides this, tests show that the seat of reserve food is not in the chroma- 
tophore but in the surrounding cytoplasm of the cell. 
The pyrenoid of Nemalion resembles those ol Hydrodictyon and 
Anthoceros in being protein in nature, staining yellow with the xantho- 
proteic test, and, with the safranin and gentian-violet stain, standing out as 
a clear refractive brilliant-red structure in the centre of the surrounding 
area, which stains a rather neutral blue with gentian-violet. There seems, 
B b 
