353 



CURRENT LITERATURE. 

 Physiology 



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. 



