330 Osborn.— Spongospor a snbterranea , ( WallrotJi ) Johnson. 
itself. This process continues for some time, so that a number of myxa- 
moebae are to be found in one cell (PL XXVII, Fig. 2). 
The amoebae are to be found in the cambium of the tuber, generally in 
the outer layers, though, in advanced stages of the disease, apparently also 
in the medullary cambium. 1 On the division of the host cell (Fig. 3) it is 
a purely fortuitous circumstance whether each resulting cell shall contain 
an amoeba, and so be infected or not. As far as my observations go, the 
whole spread of the organism from cell to cell takes place in this way. 
I have never seen any signs of the migration of an amoeba to a neighbouring 
cell, nor any continuity of protoplasm, such as Massee has described. This 
passive infection of fresh cells, or rather, handing on of the parasite to 
daughter cells in a dividing tissue, is like that described by Nawaschin 2 for 
Plasniodiophora , and Bloomfield and Schwartz 3 for Sorosphaera. 
The amoebae continue to divide as has been described, while the host 
cell increases in size, so that a late stage of infection will show many 
amoebae, now not infrequently multinucleate, occupying the greater part of 
its area (Fig. 4). The nuclei during this period divide in an amitotic manner 
much the same as characterizes the divisions in a similar stage in Soro- 
sphaera 4 and PlasmodiophoraP The chromatin arranges itself in the form 
of a ring around the karyosome, givingan appearance that has been referred 
to as the ‘ Saturn stage ’. This ring of chromatin now splits into halves 
which travel apart (Fig. 18, £), from which it will also be seen that the 
nuclear membrane has become drawn out into an elliptical shape. The 
karyosome divides by becoming elongate, then dumb-bell shape, the halves 
subsequently pulling apart ; this does not occur until the chromatin ring 
has split, a slight point of difference from the occurrences recorded in the 
other genera (Fig. 18, c , d , &c.). As the chromatin approaches the poles of 
the much elongated nucleus its constituents, derived from the halves of the 
ring and of the karyosome, blend together, and in the concluding stages 
appear as single, rounded, deeply staining masses near the poles (Fig. 1 8,/). 
Nuclear membranes form around these daughter nuclei, part of the mem- 
brane being derived from that of the parent nucleus (Fig. 18,^). It will 
thus be seen that at this stage the karyosome apparently contains all the 
chromatin of the nucleus. The chromatin granules of the latter appear 
later, and are apparently given off from the karyosome (Fig. 18, h). The 
linin network is not distinguishable until the granules are formed. I have 
not been able to determine the presence of spindles or centrosomes during 
this type of division, nor have I seen polar radiations during this or any 
1 Read, T. : Annals of Botany, vol. xxiv, 1910, p. 537. 
2 Nawaschin, S. : Flora, vol. lxxxvi, p. 404. 
3 Bloomfield, J. E., and Schwartz, E. J. : loc. cit., p. 40. 
4 See also Maire, R., and Tison, A. : Ann. mycolog., vol. vii, 1909, p. 226. 
5 See also von Prowazek, S. : Arb. aus dem kaiserl. Gesundheitsamte, vol. xxii, 1905, 
p. 39 6 - 
