Cell Structure, Growtli and Division in the Antheridia of Polytriclium etc. 163 
essential similarity in this respeet between spermatogenous and vege- 
tative cells. 
In tlie cases of other musci and of bryophytes in general, as we have 
seen, such study as has been made of the extra-nuclear Organization of 
the cell has been directed almost entirely toward determining the existence 
or non-existence of centrosomes and related structures. In view of the 
conditions now found to obtain in Polytrichum, as well as of the results 
of Marquette’s study of certain pteridophytes, it is, I think, to be ex- 
pected that further research will disclose the possession of a polar Organiza- 
tion by the cells of many bryophytes and pteridophytes in which the 
existence of such an Organization has not thus far been suspected. It is 
of importance to determine just how widely prevalent among plants is 
the unipolar type of cell structure (becoming bipolar in preparation for 
mitosis), and how frequent are the radial (as in the microspore mother 
cells of spermatophytes) and other possible types. But, as just suggested, 
it is hardly conceivable that the unipolar or other organization consists 
merely in the arrangement within the cell of those substances which happen 
most readily to take up certain stains; and the determination of the relative 
frequency of occurrence of various types of organization will be but a 
step toward a more intimate understanding of the mechanism of living 
matter. 
The Kinetosomes. 
It has been pointed out that the polar plates of the earlier androgonial 
generations sometimes seem to be made up of smaller masses closely 
packed together; and that in all probability the plates are actually com- 
posed of bodies like the kinetosomes of later generations. But whether 
or not this be the fact, there is no reason to doubt either that the plates 
and the kinetosomes are composed of essentially the same substance, 
or that they are genetically related; hence in what follows I shall speak 
generally of the kinetosomes, with the understanding that whatever may 
be said of their substance applies equally to that of the polar plates. 
Recent literature records many observations of structures, particularly 
in animal cells, which bear at least a superficial resemblance to the kineto- 
somes. This is notably true of the “chondriosomes” (“Mitochondria”, 
“Chondromiten”, “Chondriokonten”), which have been described for a 
great variety of animal tissues, particularly by Benda (1898, 1899, 1903) 
and Meves (1900, 1908, 1910). The structures referred to this dass resemble 
the kinetosomes in their staining reactions and in being, so far as yet ap- 
pears, cytoplasmic in origin and position; often, too, they are very similar 
11 * 
