1913] : CURRENT LITERATURE 161 
General biology of rusts.—Of more than ordinary biological interest is 
a paper by TISCHLER’ on the relation between Uromyces Pisi and its aecidial 
host, Euphorbia Cyparissias. As is well known, the infection of E. C yparissias 
by that rust takes place in the buds of the subterranean shoots in which the 
mycelium persists during the winter. The shoots which arise from such 
infected buds in the following spring show the characteristic deformations 
caused by the rust, but occasionally shoots are observed which outgrow the 
disease and develop normal leaves on their upper portion. This behavior 
led TISCHLER to investigate at what stage in their transition from embryonic 
to mature tissue the cells are subject to the formative influence of the fungus, 
and also to what extent such influence reaches beyond the area actually invaded 
by the mycelium. He found that the growing points of infected plants could 
be freed from the fungus by keeping the plants at a high temperature or under 
. other conditions favoring rapid development. Under such conditions the 
newly developed parts of the shoots are normal. The emancipation of the 
growing apex from the fungus succeeds more readily as the fungus approaches 
the fruiting stage, and after the aecidia are mature normal branches frequently 
develop from the infected plants if they retain sufficient vitality. Conversely, 
when the formation of aecidia is suppressed (by keeping the plants in the dark), 
it is not possible to free the shoots from the fungus. The fungus appeats to 
be incapable of further development after it has reached the fruiting stage. 
These experiments show that the meristematic tissue of the growing 
point is not subject to the formative influence of the fungus, but that such 
influence must be exerted on cells which are no longer embryonic; nevertheless 
a histological examination shows that the mycelium is present even among 
the outer layers of embryonic cells. Here, however, the mycelium is entirely 
intercellular, no haustoria being formed. As soon as the cells lose their 
strictly embryonic character, that is, as soon as vacuoles appear in them, 
haustoria begin to develop from the mycelium in their intercellular spaces. 
he formative influence of the fungus, therefore, appears to be coincident 
with the formation of haustoria. The development of haustoria the author 
associates with the formation of soluble carbohydrates whose presence can be 
shown in t e older but not in the embryonic cells. The presence of hyphae 
among the embryonic cells shows that the growing point is not protected 
from invasion by substances toxic to the fungus. 
- Regarding the general development of the fungus, the author finds that 
in the rapidly growing shoots the hyphae advance in the tracheae, by means 
of which the fungus is enabled to keep pace with the growth of the plant. 
From the tracheae the infecting hyphae enter the parenchymatous tissue of 
the cortex, pith, and leaves. The cambium, like: the embryonic cells of the 
growing point, is not infected. The formative influence of the mycelium on 


’ TiscHLeR, G., Untersuchungen iiber die eases der Euphorbia Cyparissias 
durch Uromyces Pisi. Flora 104:1-64. figs. 
