154 
Now, in the first place, the rate of development of seedlings may be 
very different for different kinds of plants, and in general it may well 
depend on this whether they are or are not susceptible to smut diseases;* 
furthermore, in the particular forms which are attacked, it may fluctu¬ 
ate noticeably according as they belong to special races or sorts, and 
consequently these are more or less receptive. But more than all this, 
in particular individuals of the same species of cultivated plant a some¬ 
what hastened or retarded development during germination will assert 
itself in smaller fluctuations, which here nevertheless may be decisive. 
For this reason it seems only natural that the receptivity toward smut 
fungi will be individually different, that consequently in the same ma¬ 
terial, under otherwise similar conditions, only a portion of the host plants 
will become smutty, as was actually the case iu our experiments. The 
fungous germs certainly penetrated into every seedling, but the growing 
point was not reached in all cases, and only those finally became smutty 
in which it was reached. To what extent the temperature may influence 
the result I will only point out briefly. Warmth hastens development, 
but whether it acts equally on the growth of the seedlings and on the 
fungous germs in them had to be decided by infection experiments con¬ 
ducted at higher temperatures than those here described. These sup¬ 
plementary experiments showed that when seedlings, as in I, were 
infected at 15 degrees C. only 6 per cent of the plants became smutty, 
while at still higher temperatures only 1 to 2 per cent appeared or no 
smutty plants whatever, t The higher temperature, therefore, hastens 
the growth of the seedling proportionately more than that of the fun¬ 
gous germ, and thus hinders the development of smut in the plants. 
It now remains to ascertain the reasons why, in all the series of experi¬ 
ments, not a single one of the infected barley seedlings produced a smutty 
plant. In the first place, it is self-evident that the negative results with 
the barley can not change in the least the positive results with the oats. 
On the other hand, without further inquiry, the explanations given for 
the incomplete sickening of the oat plants are by no means to be urged 
* From the sum of the experiments and the preceding observations it follows 
naturally that the simple penetration of the germ into the host plants, on which the school 
of De Bary laid such stress, is not decisive for the appearance of smut diseases. But 
beyond this, I have by special experiments determined that the most diverse smut germs 
can penetrate into all sorts of plants, which are never attacked by smuts, consequently, 
the penetration of the germs only proves an unimportant detail. The results of these 
many experiments establish the accuracy of the views and conjectures on parasitism 
and the way it may occur in nature, of which I have already spoken in Den Brand- 
pilzen i, p. 26-29. 
tin the paniculate heads of the oat, sound spikelets sometimes occur at the tip of 
a panicle while the lower spikelets are destroyed by smut. In such cases the pene¬ 
trated smut germs had not reached the uppermost point of the inflorescence when 
tbe elongation began; therefore these remained sound while the lower were attacked 
by smut. The correctness of this interpretation of the interesting discovery is shown 
by the fact that in such partially diseased panicles the uppermost portions without 
exception are sound and the lower are diseased, but never do the upper become diseased 
while the lower remain sound. 
