BOOKS AND CURRENT LITERATURE 



215 



substance ''X." Night temperatures are however important in favoring 

 growth especially during the first half of the growing season. 



The march of stomatal behavior was obtained by means of the 

 stomatograph. The stomata begin to open at sunrise, reaching their 

 maximum at about 9 a.m. By noon closure is complete, no subsequent 

 opening having been observed. The maintenance of moderate aper- 

 ture, and a slower closing on cloudy days is attributed to illumination 

 "as there is no water-shortage." The results are taken (perhaps some- 

 what conditionally) to indicate that water-shortage is the direct cause 

 of stomatal closure, a view supported bj' the reviewer's own work. He 

 found the stomata to close at a time coincident with the partial wilting 

 of the leaf (involving a net water-loss) and this quite earh- in the day — 

 9 to 11 hours. 



Concerning transpiration Balls has little to say, the only data supplied 

 are those obtained by initial weighing of removed leaves. He has 

 avoided the potometer method, which, in the reviewer's experience, has 

 no small value in as severe a climate as that of southern Arizona. Balls' 

 data furnish, however, the indications that transpiration is "practically 

 in abeyance at night and early morning," has reached the maximum 

 by 9 to be retained till past noon, in spite of the fact that the stomata 

 are nearly closed. Here the stomata are i^ot the limiting factor; de- 

 creased humidity and higher temperatures increase evaporation, and 

 hence maintain the transpiration rate. 



Of particular interest to the reviewer is Balls' studj' of boll shedding. 

 Prime interest centers in the correlation between shedding and the 

 position of the water table. Obvious is the meaning of this in regard 

 #to the effect of irrigation which ha*s been found in Egypt to bring up 

 the water table to a level inimical to the cotton plant. Those familiar 

 with the fate of non-drained and over-irrigated areas will see here a 

 case of first importance in exemplification of the principle that the whole 

 of the problem of making the desert blossom as the rose is not merely 

 in adding water to the soil. Balls concludes then that boll shedding 

 intervenes as a result of the asphyxiation of the roots and a consequent 

 limiting of water supply. The reviewer has in hand evidence that the 

 shedding is directlj' a consequence of limited water supply to the boll 

 (and is so far in harmony with Balls), but that the more immediate cause 

 lies in the anatomical and morphological relations of the boll to the 

 shoot bearing it. The water supply is thereby readily limited, even 

 . though the soil water conditions are favorable enough — evidence for 

 which is in process of preparing for publication. The reviewer must, 



