399 BOTANICAL GAZETTE [OCTOBER 
element with exosmosis. Curves representing the equation derived thus on 
theoretical grounds resemble in type those obtained in actual experiments. 
The methods used in this work seem admirably adapted to a crucial test of 
CzarEk’s theory, which seems entirely untenable in view of the evidence 
submitted.—Cuart-es A. SHULL. 
Desiccation.—An investigation of the course of desiccation and partial 
starvation in cacti has been made by MacDovucat, Lone, and Brown.’ The 
principal studies center upon the changing rate of water loss, chemical changes 
in the food reserves, plasmatic colloids, and cell sap, and the morphological 
changes which occur during long periods of desiccation. In one case a large 
Echinocactus was under observation for 6 years after removal of the plant 
from the soil. Water loss is rather rapid at first, but proceeds more and more 
slowly with time. While ro per cent of the water was lost the first year in 
one specimen, during the sixth year only 5 per cent of the water remaining at 
the beginning of that year was lost. The loss of water is much more rapid 
of course in the open than in diffuse light and Echinocactus can withstand 
desiccation not more than 2 years with free exposure. 
The chief chemical changes noted during the starving period concern the 
carbohydrates. The density of the cell sap decreases, due to disintegration of 
the carbohydrates, and the reducing sugars are found mainly in the inner part 
of the cortex in desiccated specimens rather than near the surface as in normal 
plants. The total amount of reducing sugars decreases during desiccation, 
while non-reducing sugars are increased noticeably in the cell sap. Reduction 
of the amount of sugars leads to reduction of acidity if the light intensity is 
sufficient for photolysis of the acid. In weak light even, if the sugars run low, 
the acids may accumulate because of the absence of photolysis. Differences 
in acidity are thought to be partially responsible for differences in the colloid 
hydration and swelling of tissues when placed in water. 
The main morphological changes consist in thickening of the cuticle, thin- 
ning of the anterior walls of the guard cells, partial destruction of the plasmatic 
colloids, shrinkage in the size of the nucleus, and especially the development of 
cortical lacunae through hydrolysis of the cell walls of this region of the stem, 
The vascular tissues are not affected, and the medullary cells much less than 
the cortical cells —CHartes A. SHULL. 
The vegetation of Michigan.—From the data obtained during a few wee eks 
in Michigan, Harper” has listed the principal plants in the order of their 
abundance and has discussed certain features of the environment. He recog- 
nizes but two types of succession, the one from the filling up of lakes and other 
a MacDoveas, D.T., Lona, &. R., and Brown, J. G., End results of desicca- 
tion and respiration in siocsiieat plants. Physiol. Res. 1:289-325. 1015. 
Harper, R. M., The plant population - saben lower Michigan and its 
environment. Bull. Torr. Bot. Club 45:23-42. 
