Bailey . — Puccinia malvacearum and the My coplasm Theory . 175 
Seed sown in September germinated the same year, and the young 
plants, if kept in boxes in a cold house during the winter, did not show any 
trace of disease till the following May. 
2. Limitation of disease outbreak to leaves of a certain age. ‘ Primary * 
and ‘ secondary ’ development. Eriksson calls attention to the fact that the 
leaves of affected plants show little or no infection whilst young, but when 
they arrive at a stage approaching maturity they become densely covered 
with pustules of the rust. Leaves that escape infection at this time never 
seem to become heavily infected. 
The conclusion that Eriksson draws from these observations is that the 
sudden appearance of great quantities of qustules on the middle-aged leaves 
represents the separation of the mycoplasm existing within the leaf tissues 
and its differentiation into vegetative and reproductive mycelium. The 
sporadically distributed pustules appearing on leaves of various ages he 
attributes to outside infection. These observations have been confirmed in 
part by the present writer, but the conclusion drawn is that the metabolism 
of the middle-aged leaf is such as to render it much more susceptible to 
attack than younger or older leaves. This conclusion is supported by 
observations made in the present season on the incidence of rust upon wild 
plants of Malva sylvestris . 
About a dozen plants altogether were found and marked for future 
record. These will be referred to by letters as shown below : 
‘ A.’ Four plants growing within a radius of 8 feet of one another. 
‘ B.’ Two plants growing close together at a place half a mile distant 
from ‘ A 
‘ C.’ Two plants close together about half-way between ‘ A * and ‘ B ’. 
‘ D.’ Five plants scattered at long intervals over an area situated almost 
a mile from any of the above. 
When first observed, on the jqth of May, one of the ‘ A ’ plants showed 
a few young pustules on four leaves (one of which was still quite young). 
One leaf of one of the 1 C ’ plants was similarly affected. 
On May 20 all the middle-aged leaves of the plant of the ‘ A ’ group 
mentioned above were affected, carrying an 'average of 30 pustules apiece. 
Some of the younger leaves of the same plant also showed a few pustules. 
The plant nearest this one in the same group showed a few pustules 
sporadically distributed. The infected plant in the ‘ C ’ group showed 
a slight general increase of disease. None of the other plants showed 
disease. 
On May 26 the first infected plant in ‘ A * group showed dense masses 
of pustules on all its middle-aged leaves and sporadic infection on most of 
the younger and some of the older leaves. The plant next to it was in 
practically the same condition, and both answered the description of 
‘ primary infection 5 given in Eriksson’s paper. Of the other two plants in 
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