Chapter X — 203 — Loss and Retention 



in water content of leaves have also been carried out by Rywosch (1908), 

 MoLiscH (1921), ScHROEDER and Horn (1922), Tollenaard (1925), 

 and Collorio (1928). That this conversion of starch is associated with 

 the increase of amylolytic activity during water deficit and apparently not 

 with a pH shift was shown by the quantitative investigations of Spoehr 

 and MiLNER (1939), Table 48. 



In spite of adequate soil moisture, the desiccating effects of hot dry 

 winds may halt the accumulation of dry substance due at least in part to 

 the closure of the stomata. The previous conditions under which a plant 

 has been grown will influence this response. Thus stomatal closure in 

 wheat grown in soil at 70% of its water-retaining capacity was evidenced 

 when water reached 40 to 50 per cent of this value. Stomata of wheat 

 grown in soil at 40 per cent of its water-retaining capacity were always 

 open (Vassiliev, 1929; Kondo, 1931). The difficulty of maintaining a 

 soil at any moisture content below field capacity throws doubt upon the 

 results of such experiments (Veihmeyer, 1927). Kransosselsky-Maxi- 

 Mov (1930) found redistribution of water from the inflorescence to leaves 

 in plants subjected to artificial dry wind even when they were growing in 

 well watered soil. Stomatal closure also occurred. 



Several workers have found that water deficit per se tends to cause 

 stomatal closure (Iljin, 1923; Stalfelt, 1932; Scarth, 1932). In the 

 guard cells dehydration tends to cause conversion of sugar to starch, ac- 

 cording to the work of Iljin (19226) and Steinberger (1922). This is 

 in harmony with the observations of Spoehr on the carbohydrate ratio in 

 cacti but contrary to the general trend of increased hydrolytic amylolytic 

 activity during drying found in most plants. It appears, however, that 

 turgor loss induces a pH reduction in guard cells, which condition is con- 

 ducive to the sugar-to-starch transformation. 



Huber (1937) has emphasized the profound influence that water has 

 on the life processes of plants. In the field of genetics he refers to the 

 work of Oehlkers (1937), and Kisch (1937). Oehlkers and his co- 

 workers have shown that water deficiency during the conjugating phase 

 of reduction division decreases the number of the terminal junctions and 

 chiasmata, as shown in Table 49. 



Table 49. — Influence of zcater absorption on vieiosis in Oenothera {data of Kisch 



and Oehlkers after Huber, 1937) : — 



Osmotic value 



of inflorescence decrease in chiasma 



Treatment atm. frequence in % 



Normal 6.5 4.71 



3 days dry 9.4 4.60 



5 days dry 9.7 13.42 



7 days dry 12.6 20.31 



Huber also points out that at least part of the effect of low temperature 

 in inhibiting conjugation may be attributed to water deficiency as the effect 

 vanishes when water is supplied in sufficient quantities. 



Subaqueous Transpiration : — It is commonly agreed that water move- 

 ment through the xylem system results either from root pressure or trans- 

 piration pull. In a normally transpiring plant water loss causes a diffusion 

 pressure deficit in the wall colloids of the mesophyll, sufficient to explain 



