No. 3, December, 1920J PHYSIOLOGT L99 



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proportion of li])ins, with the inevitable small amounl of salts." Growth is defined as "hy- 

 dration of colloidal material in a living condition" usually accompanied by increase in the 

 colloidal mixture. As organs mature, the relative dry weighl often increases, but in succu- 

 lent plants the reverse is true due to the conversion of hexoses into pentosans which have 

 a higher water capacity. Protoplasm may be considered as composed of two elements, the 

 pentosans and the albumins, the hydration of the albumins being increased by increase in the 

 hydrogen ion concentration and the pentosan decreased. Amino compounds increase the 

 hydration of the artificial colloidal mixtures as well as increase the growth of plants in cul- 

 tures. The mechanism of the increase of cell size is related to the assumption that the more 

 solid phase of the cell contents would take the position of the outer layer and tend to increase 

 faster than the liquid phase. The inter-relationships of the constituents of the solid and 

 liquid phases of the colloidal protoplasm might form a kind of mosaic membrane, but it would 

 be a membrane resulting from the product of the surface energy of the protoplasmic mass 

 and that of the medium and would have "no other permanent or morphological value." 



In the study of the effects of organic acids and their amino-compounds on growth the 

 following colloids — agar, gelatin, agar-gelatin (8:2), and agar-oat-protein (8:2) — were tested 

 at 16-17°C, for the amount of expansion from a dried thickness to complete hydration. The 

 gelatin-asparagin test and the agar-gelatin-asparagin test are inconclusive due to the dis- 

 persion of the gelatin. 



The various colloid combinations swelled, in general, in solutions of glycocoll at rates 

 equal to or greater than in water. When glycocoll was combined with acetic acid the rate was 

 reduced, with one exception, somewhat below that in the acid alone. It is shown by experi- 

 ment with plant tissues that because of their complex nature no prediction of the effect of 

 temperature changes upon imbibition can be made. In general "the increase in swelling in 

 distilled water is seen to be about twice that in the acid in the rise from 18°C. to 38°C. The 

 walnut fruit, as a type of a tissue which shows an increasing dry weight with age, and the 

 tomato, which shows an increasing relative moisture content as it matures, were studied. 

 Auxograph records of the course of development of the walnut shows that the increase in size 

 is irregular, being dependent upon the ratio between transpiration and absorption. Actual 

 shrinkages appeared when transpiration exceeded absorption. Similar results were recorded 

 in the growth of the tomato. In both, when the increased temperature caused increased trans- 

 piration which was not offset by other conditions, the rate of growth decreased or shrinkage 

 occurred. The percentage of water in the nuts was usually higher than in the twigs and stems 

 which bore them. In fleshy, flat joints of Opuntia decrease was demonstrated at night and 

 increase in growth coincident with the rise of temperature during the day. Decreased acidity 

 in cells showing high pentosan content during the light period is given as the reason for this 

 condition. — Ernest Shaw Reijnolds. 



1346. MacDougal, D. T. The physical factors in the growth of the tomato. Bull. Torrey 

 Bot. Club. 47: 261-269. 1920. — Observations on growth in the fruits of the tomato showed 

 that they could be used as an example of development and growth without increase of dry 

 weight. The rate of increase in diameter is not a measure of the actual accretion of water 

 and solid material; furthermore, its culmination may not be reached until the fruit approaches 

 maturity. The conclusion is made that in young fruits, the low salt content and acidity give 

 a set of conditions in which imbibition is the chief distentive force, and in older fruits the 

 higher acidity and salt content make osmotic action more important. — P. A. Mum. 



1347. Reed, H. S., and F. F. Halm a. The evidence for a growth-inhibiting substance in 

 the pear tree. Plant World 22: 239-247. 3 fig. 1929.— The authors discuss the growth habits 

 of new pear shoots, and present evidence in favor of the hypothesis that growth-inhibiting 

 substances are generated in the apical portion of the shoot, which travel toward the base of 

 the shoot, and maintain dormancy of the lateral buds. Horizontal shoots show the inhibi- 

 tion chiefly along the ventral side, while dorsal buds show considerable growth. Buds between 

 dorsal and ventral position show intermediate growth. They take this behavior to indicate 

 that the growth-inhibitor accumulates along the ventral side of the shoot, and thus frees the 

 dorsal buds from its influence. — C. A. Shull. 



