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MacDougal, D. T., H. M. Richards, & H. A. Spoehr. Basis of suc- culence in plants. Bot. Gaz. 67; 405-416. 1919.

Succulence is defined as an exaggerated development of the parenchy- matous regions of the plant. The masses of thin-walled cells become permanently distended and tuigid. Succulent plants are characteristic of deserts and of salty areas along seashores. All attempts to connect the origin of succulence with the presence of salts in the soil, or with high acidity in the plant tissues, or with purposeful development of water-storage tissue have been inadequate.

The authors found a plant, Castilleja latifolia, becoming a succulent on dry bluffs along the coast of California, but producing thin leaves in places with better water supply. The thin leaves show double the acidity of the succulent leaves. " From a large series of experiments, analyses, and obser- vations, they conclude that with scarcity of water in the cells, polysac- charides are transformed into pentosans. The polysaccharides show little imbibation, while the pentosans show an enormous capacity to imbibe water and to swell. The result is the production of a succulent plant, and as the reaction is irreversible, the succulence is permanent. They believe that the high acidity is nothing more than a characteristic of plants which have a metabolic complex favorable to the formation of pentosans, and to the development of succulence under certain conditions of environment.

Winfield Dudgeon.

Gray, John and George J. Pierce. The influence of light upon the action of stomata and its relation to the transpiration of certain grains. Am. Jour. Bot. 6 : 131—155. 18 figs. 1919.

It is commonly accepted that stomata act as the main regulators of transpiration, and that their movement is due to changes in the turgidity of the guard cells. From a study of a number of cultivated and wild grasses the authors conclude that while " turgidity of the guard cells is a necessary

factor in producing and maintaining their elasticity the direct and indis-

pensible agent in controlling the opening and closing of the stomata is sunlight, which acts as a stimulus on the guard cells themselves." They find that the stomata do not maintain sufficient turgidity to be affected by light when the soil moisture falls below a certain specific amount, but no matter how well watered the plant is, the stomata do not open on cloudy days. When sufficient moisture is present, the opening of the stomata follows very closely the incidence of sunlight.

Their method was to examine the leaves under a microscope while still attached to the growing plant. This involves minimum disturbance of the stomata, and permits repeated examination of the same leaf, and even of the same stomata, under varying conditions.

Winfield Dudgeon.