430 BOTANICAL GAZETTE [JUNE 
fungus may work in one or more ways to diminish transpiration, 
either by its intoxicating action upon the host cells or by causing 
hypertrophy which alters the normal activities of the leaves. 
Each of these problems is at present the subject of further investi- 
gations. Without going into a study of the cytomorphology of 
the diseased leaves at ‘this time, it may be said that the portions 
of the apple leaves bearing cluster cups are three to four times 
the normal thickness. Their hypertrophy is, as REyNoLps® has 
reported, chiefly the result of changes in the spongy tissue (paren- 
chyma), by which the loose tissue with large intercellular spaces 
is replaced by large columnar cells with no intercellular spaces. 
Stomata are scarce or lacking and the substomatal cavities are 
altogether lacking. This closure of the intercellular spaces of the 
leaf diminishes the opportunity for water elimination from the 
interior of the leaf and consequently affects the transpiration. 
This may account for the difference between our results and those 
of BLODGETT previously cited. In the case of the leaves attacked 
by G. interstitialis, the destruction of the lower epidermis facilitates 
loss of water; while in the apple leaves attacked by Gymnospo- 
rangium Juniperi-virginianae, the hypertrophy obliterates the 
stomata and retards the elimination of water. 
The retardation of transpiration in the apple leaves studied 
is believed to have some significance for the study of the real 
problems concerned with this disease. It has for a long time been 
known that transpiration and growth are intimately associated. 
Growth does not usually occur without transpiration. LivincsToNn’? 
and others have shown that in certain instances, at least, transpira- 
tion is a reliable index of growth. 
Further studies are being made upon the economy of diseased 
_ trees, but it is considered that the decreased transpiration of leaves 
affected with the cedar rust is one factor which may account for 
the bad physiological condition of such trees. 
VIRGINIA AGRICULTURAL EXPERIMENT STATION 
BLACKSBURG, VA. 
6 Reynotps, E. S., Studies of parasitized leaf tissue. Bor. Gaz. 53: 365. 1912. 
7 LIVINGSTON, B. E,, Relation of transpiration to growth in wheat. Bor. Gaz. 
40:178. 1905. 
