CYLINDROSPORIUM ON STONE FRUITS I5I 
chalky spots on the sixth day. Infection did not occur in any case 
where the spores were placed on the upper surface of the leaves. 
When this paraffined material was cut and stained no mycelium 
was found within the leaf tissue killed the third day. By the end of 
the fourth day some germ tubes had entered and had formed quite 
extensive mycelium. When these mycelial threads, entering the 
stomates of the lower epidermis and traversing the mesophyll, come 
in contact with the upper epidermis they branch profusely and form 
by the end of the fifth day a very delicate stroma with conidiophores 
and young conidia. By the end of the sixth day conidia have matured 
in sufficient numbers so that the pressure ruptures the leaf epidermis 
above the stroma. 
No haustoria were found until the fifth day. The host cells appear 
normal until the sixth day, when, in a few cells just beneath the stroma 
and in contact with it, the protoplasm was slightly shrunken, due 
probably to drying. This appearance spreads rather rapidly after 
the epidermis is broken. The leaf tissue containing the fungus is 
separated off by the enlargement of certain cells mentioned above and 
the separated tissue yellows rapidly. The length of time varies, but 
usually within 7-10 days after infection the spots begin to yellow and 
drop out. 
An apparently related case to this shedding of the diseased spots 
is that reported by Galloway (12) in which the needles of Pinus 
virginiana drop off after the formation of Coleosporium pustules. 
Galloway says that this casting is not caused by the fungus directly 
but by the loss of water through the break in the epidermis. 
Enlargement of Cells of Absciss Layer. — To explain the enlargement 
of the cells of the separation layer, four hypotheses have been sug- 
gested, viz.: First, the release of tension due to shrinking of the 
adjoining cells may allow the cells to enlarge ; second, the cell walls may 
be softened by some enzyme secreted either by the fungus or by the 
host protoplasm, thus allowing the cells to expand ; third, the colloids 
of the cell (protoplasm, cell wall, etc.) may be so modified as to have 
a greater affinity for water; and fourth, the osmotic pressure may in 
some way be increased in these cells. Of the four the last seems to 
be the most plausible, and while it is not yet proven beyond doubt 
all observations seem to support this as an explanation for the 
phenomenon. 
The first hypothesis is invalid because these cells begin to enlarge 
