22 Research Bulletin No. 1 
acters there can be no reason why the characters decided upon 
by Appel and Wollenweber should not give a good working basis 
for the genus. 
In this fungus not much difference can be noticed in the 
rapidity of the growth of the cultures, whether one begins with 
conidia or with mycelium as inoculum. It was noted that a 15- 
months-old culture on rice which was as dry as powder gave 
viable conidia, which had not at all lost their pathogenesis for 
tubers. 
The spore walls are quite thick. Single-celled or rwo-celled 
colonies are by far more resistant to collapse of the wall than 
those of a higher number of cells; in fact it seems probable that 
the walls which set in in a growing cell are a response to a pres- 
sure stimulus. The diameter of septa suffers practically no 
shrinkage even under the driest condition and consequently 
gives a very constant and reliable basis for measurement. When 
the rell wall of a spore collapses, the spore looks very much 
like a series of hourglasses (PL XXVII. figs. 14-15, 20, and 22). 
When the fungus is grown on agar, the cells swell greatly 
while the septa do not, and then we get a spore which looks very 
much like an inflated rubber tube constricted by bands at regular 
intervals. Sometimes these appear in colonies on agar and are 
then associated with a slimy appearance so that one could easily 
mistake them for a new species or for a subspecies. Tn fact, 
both the dried-out form and this swollen form have off and on 
been described as new species. 
If the spores figured by Appel and Wollenweber 191 <». page 38, 
as Fusarium didymwm were bent slightly on the cross wall as an 
axis, and if one end were bent a trifle more than the other, we 
would have a spore such as presented by Fusai 'nun tuberi- 
rorum. In the one-septate spores one end usually is a little more 
plump than the other. Some of these spores, however, show a 
true sickle shape. By far the most spores in the pure cultures, 
even as many as 98 per cent, are one-septate. At times the basal 
ends show remnants of the so-called foot, but it is a very diffi- 
cult matter to decide which end is basal or apical after the spore 
is once off the sterigma. 
Some of the higher septate spores show the shape of Fusarium 
ooeruleum, others that of Fusarium sp. (Appel and Wollenweber 
1910, fig. S, page 38). A combination of Fusarium coeruleum 
and of Fusarium solani would in many cases give us the shape 
of the typical spore of Fusarium ttiberivorum. Often the non- 
septate spores are clavate. This condition is very frequently 
found on beef bouillon or in cultures which have been grown in 
distilled water (PL XXVII. fig. 13). When colonies or spores 
are put into water all of the spores are of the clavate shape. 
