

162 BOTAMCAL GAZETTE [august 



of time. Again, a slight curvature may accelerate the growth on the upper 

 side of a dicotyledonous stem, whereas a more pronounced bend may produce 

 eccentricity upon the under side or inhibit the growth of both the upper and 

 under sides and lead to lateral eccentricity. 



In the fifth and concluding section of the volume, Jaccard elaborates the 

 following hypothesis: "The morphological characters common to all trees are 

 determined (i) by the polarity of their organs, that is to say, by their tendency 

 to grow most rapidly in a vertical direction, and (2) by the modifications 

 which the exigencies of nutrition and the action of external forces (gravity, 

 heat, light) impress upon this polarity. These modifications manifest them- 

 selves through the osmotic force of cells which engenders, on the one hand, 

 two circulatory currents (the ascending sap and descending current of elabo- 

 rated substances), and, on the other hand, mechanical strains and stresses 



a 



(pressure of turgescence) capable of influencing the form of cells In 



general, such variations in gross form and anatomical structure, as may be 

 observed at different levels in the concentric, vertical axes of trees, are deter- 

 mined by the physical conditions of the transpiration stream and the flow of 

 elaborated sap. On the contrary, the anatomical differentiation and varia- 

 tions in transverse sections, which are concomitants of the eccentric growth of 

 inclined or horizontal branches, are due to mechanical forces engendered by 

 the unequally rapid growth of the antagonistic sides of these organs, under 

 the asymmetrical influence of gravity and light." 



Although the author is justified in contending that the problem of the 

 growth and form of stems and branches should be attacked from the point of 

 view of fundamental physiological phenomena, and in rejecting teleological 

 conclusions as unscientific, he extends his own generalizations much farther 

 than is warranted by his experimental data. When one considers how little 

 is actually known about the "ascent of sap," the growth and activities of the 

 cambium and its derivative tissues, the distribution of food substances and 

 osmotic pressures, and, in general, concerning transpiration, metabolism, and 

 translocation and their interactivities in arborescent plants, one is inclined to 

 question whether there are available at present sufficient reliable data to form 

 the basis for such a comprehensive hypothesis as is formulated by the author. 

 I. W. Bailey. 



Factors of fruitfulness. — A contribution by Wiggins 6 covers investigations 

 for 5 years, chiefly upon trees that were 8 years old at the beginning of the 

 experiment in 19 13. Attention was centered upon the individual fruiting 

 branch "in an effort to determine the effect of certain conditions and practices 

 upon the development and performance of the individual fruit spur. 



The data for the performance of the individual spurs were obtained 

 from 8-year-old Rome, Gano, Winesap, Grimes, York, and Jonathan. The 

 first selection was made of fruiting spurs, but after that a blossoming spur was 



6 Wiggins, C. C, Mo. Exp. Sta. Research Bull. no. 32. 1-60. 1918. 



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