1919] AGRICULTURAL BOTANY. 27 



process of hardening young leaves seem to pass rapidly through some sort of 

 maturation process. 



Frozen cells in the leaves of cabbage, Bryophyllum, salvia, and lettuce were 

 found to be stimulated to growth and to produce tumors similar to those in 

 pathological conditions but without the presence of bacteria. Frozen spots 

 on the leaves of tomato, coleus, geranium, and a number of other plants did not 

 receive a growth stimulus but were killed by the freezing. The peroxidase 

 content of the intumescences in the case of cabbage was found to be much 

 greater than for the normal 'tissue. A decrease of hydrogen-ion concentration 

 may occur in such cells, and this condition is believed to allow greater activity 

 or accumulation of the respiratory enzyms, particularly peroxidase. 



The principal effect of the hardening process on cabbage is believed to be a 

 change in the constituents of the protoplasm which prevents their precipitation 

 as a result of the physical changes incident upon freezing. The proteins are 

 changed to forms which are less easily precipitated, as indicated by an increase 

 in the amino-acid content of cabbage plants on hardening. Cabbage plants 

 which had become resistant to freezing through the hardening process showed 

 only slight changes in carbohydrates, and it is considered that the prevention 

 of protein precipitation by sugar accumulation during hardening is not suffi- 

 cient to account for the resistance of hardened plants to freezing. The pro- 

 teins of the midrib of cabbage leaves were precipitated more rapidly than those 

 of the rest of the leaf, and this is considered to be due to physiological differ- 

 ences between vascular and other tissues of the leaf. In the juices of non- 

 hardened leaves of cabbages, the proteins were found to be precipitated to a 

 greater degree by freezing than in those of hardened cabbages, the percentage 

 of precipitation on freezing being closely paralleled by the relative precipitation 

 on the addition of acid. The effects of desiccation, freezing, and plasmolysis 

 are considered to be similar, in that all these processes cause changes in the 

 hydrogen-ion and salt concentrations. 



The transpiring power of plants, Edith B. Shkeve (Carnegie Inst. Washing- 

 ton Tear Book, 16 (1911), pp. 66-68). — Studies reported so far as carried in 

 comparing the index of transpiring power as determined with cobalt tripartite 

 slips of standardized paper with the transpiring power as determined by the 

 rate of loss of weight from the plant to that from an atmometer showed the same 

 general curve except that the time of beginning of incipient drying can be de- 

 tected sooner by the cobalt slips than by the weighing methods, and as accu- 

 rately and more reliably, as the cobalt method can be used with plants naturally 

 rooted in the earth. An attempt is being made to lessen the largest source of 

 error, which lies in the assumption that the leaf temperatures agree with air 

 temperatures. 



It has become evident that a comparison of the transpiring power of different 

 species or strains necessitates finding the whole dally march of transpiring 

 power, isolated readings by either method having but little value. It is neces- 

 sary also to test several leaves of the ages and sizes represented. 



The relation between water loss by evaporation and water gain by absorp- 

 tion in colloidal gels, Edith B. Shkeve (Carnegie Inst. Washington Year Book, 

 16 (1917), pp. 68-71).— Preliminary experiments (E. S. R., 35, p. 733) on Opuntia 

 versicolor showing the probability of a direct relation between the power to ab- 

 sorb water and the power to withhold water against atmospheric evaporative 

 forces have been confirmed by further experimentation on this species and 0. 

 blakeana (?). Work testing this relation for colloidal gels has been planned, 

 and tests have been made with gelatin, the absorption rate of which proves to be 

 influenced greatly by Its history in ways which are detailed, so that certain pre- 

 cautious must be observed in order to obtain comparable results. The conclu- 



