1916] CURRENT LITERATURE 245 
thrown into rest periods at the winter period of minimum light if they were 
pot bound, but not with good salt supply. The part played by specific struc- 
ture was evident here, for light amounts that produced continuous unfolding 
in buds of Terminalia gave buds that did not unfold in Theobroma, and complete 
rest in Eriodendro 
Intense photosynthesis resulting in high carbohydrate supply produces 
rest if salts are insufficien ne growth period may exhaust the salt supply, 
thus producing rest nie lasts until the salt supply rises because of non- 
consumption and induces a second growth period. KLEBs suggests that this 
is the condition that throws into dormancy the buds formed in the spring on 
trees growing in our climate. The salts have been reduced by the formation 
of stems and leaves and the carbohydrates are abundant, owing to the activity 
of the newly formed leaves. He suggests that high photosynthesis along with 
low salt supply may produce dormancy in a similar way in trees of the tropics 
Several workers have shown that older individuals of a tropical species are 
more likely to show a rest period than young ones. This Kiess attributes 
not to age so much as to limited nutrients conditioned by a multiplication of 
buds dependent upon a single absorptive and conductive system. 
KLEBs criticizes Jost and Srmon for classifying salts with anesthetics as 
mere stimuli to growth, rather than thinking of their nutrient significance. 
He speaks of salt addition as a quantitative increase of an already present 
and absolutely necessary growth factor. In this connection he emphasizes the 
error of assuming that the soil is.a constant factor. In such a complex 
system of organisms and organic and inorganic materials in ever shifting 
equilibria one must expect periodic changes in supply of nutrient salts as well 
as in other factors. The frequently observed fact that different individuals 
of the same species in the tropics show marked differences in vegetative 
periodicity may be due to the soil factor. 
Kiess speaks of throwing Pithecolobium into rest at will (by salt reduction) 
or active growth (by salt addition) with the same sort of ease as Vaucheria can 
be caused to reproduce by zoospores on the one hand, or by oospores on the 
other; or water to assume the form of a solid under one condition and that of 
a liquid under another condition. His evidence leaves little doubt that the 
tropical trees in general can be made to behave quite like Pithecolobium. I 
ms that Kress has established his general contention of the dual deter- 
mination of periodicity in these forms, but there are some minor conceptions 
that are less happy. 
He classifies all nutrient salts together as if they all have the same effect 
upon the course of development, while agriculturists have fully demonstrated 
that nitrates and phosphates in some respects have opposite effects. He 
implies that salts have their effects mainly as nutrients (building materials), 
while the extensive work on antagonism probably deals with general physical 
or colloidal effects, and there is evidence that metallic ions are of importance 
in catalysis. Moreover, it is not yet shown whether high nitrate supply induces 
