Recent Work on Endotrophic Mycorhiza. 169 
From comparison of plants of the same species, e.g., Arum 
maculatum, Gallaud could find no difference between infected and 
uninfected plants attributable to infection. He held, moreover, 
that the communication between the internal and external systems 
of mycelium is too scanty to support Stahl’s view as to the role of 
the fungus in absorption. 
No definite relation of cause and effect was established between 
infection and the production of root hairs. 
The physiology of the relationship is discussed at some length 
and the facts interpreted as follows. It is believed that mycelium 
living in the soil is attracted chemically by the roots and becomes 
closely applied to them. Hyphae penetrate either directly or at 
special cells and there is evidence that penetration is resisted by 
the plant-cell. This mycelium is invariably intracellular in the 
outer cortex. In the inner cortex near the vascular cylinder, it 
forms well-developed haustorial organs ( arbuscules ). Abundance of 
food-material so obtained leads to the formation of reserve organs 
at the ends of young hyphae {vesicles), which can serve for immediate 
growth, or function ultimately as reproductive organs after the 
death of the plant. There is evidence of resistance to invasion on 
the part of the plant-cells, passively by the deposition of membrane 
over invading hyphae, and actively, after invasion, by digestion of 
the intracellular suckers ( arbuscules ) transforming them to structure¬ 
less organs ( sporangioles ). These organs {arbuscules and sporan- 
gioles) are regarded as representing two stages in the development 
of the same structure and as the physiological homologues of the 
“ pilzwirthzellen ” and “ verdauungszellen ” of the orchids. 
Active digestion of the mycelium is confined to certain cells 
and is characterized by definite cytological changes affecting the 
nucleus and other cell-organs. After digestion the cytoplasm and 
nucleus again become normal. There is good evidence of absorption 
of starch by the fungus, but the plant ultimately recovers the 
greater part of the absorbed material, albeit possibly in an altered 
form. 
Gallaud was led to believe that in the types of mycorhiza he 
describes, as compared with the much more advanced orchid-type, 
there is no true symbiosis, (“ symbiose harmonique”) between 
plant and fungus. The latter he regards as a special kind of 
‘ internal saprophyte ’ of the roots. 
In view of the facts described, this use of the term saprophyte 
is misleading, and it would seem more intelligible to describe 
the invaders as internal parasites of a special kind whose further 
