4 SALMON : SUPPLEMENTARY 
way. The bounding membrane of the sheath, on the other hand, 
is the plasmic membrane of the host cell stretched and greatly 
enlarged by the osmotic forces involved.”’ 
The haustoria of Frysiphe graminis are, as is well known, 
peculiar in being provided with long finger-like processes. These 
haustoria Smith has studied in detail, and shown well in several 
figures. With reference to these haustoria it is observed, «this | 
form of absorbing organ may be looked upon as the result of a 
special effort of this species to obtain abundant food. The heavy 
growth of mycelium and the immense number of conidia produced 
by this species show the success it has attained. * * * Certainly 
these haustoria give an impression of activity not gained from 
other Erysipheae.”’ 
The most interesting discovery of Smith, however, is in con- 
nection with the haustoria of Uncinula salicis. Examples of U. 
salicis on Salix discolor were used for investigation, and the de- 
velopment of the haustoria was found to take place as follows: 
The mycelium (proper) is entirely external ; on the upper surface 
of the leaf the lobed appressoria give rise to penetrating tubes 
which enter the epidermal cells. All of these tubes, however, do 
not (as in all other cases known) develop in the epidermal cells 
into haustoria. Although normal haustoria are formed abundantly 
in these epidermal cells, in addition numerous slender hyphae can 
be observed reaching from the outer walls across the epidermal 
cells to their inner walls. These hyphae are the penetrating tubes 
or necks of subepidermal but otherwise normal haustoria in the 
palisade cells. On the lower surface of the leaf, in a similar man- 
ner, some of the penetrating tubes reach into the mesophyll cells 
immediately under the epidermal layer, and form haustoria there. 
Smith has also investigated the intercellular hyphae of Phy//ac- 
tenta, and has found that occasionally the hyphae produce haustoria 
in the palisade cells. It was observed that the majority of the 
intercellular hyphae (which may consist of three to five, or perhaps 
more, or rarely of only two cells) take a more or less direct course 
towards the vascular bundles—a region abundantly supplied with 
available food ; the fungus therefore shows a selective chemotropism. 
Examples of Phyllactinia on Xanthoxylum Americanum were 
found to offer some striking differences with respect to the develop- 
