EDGAR TULLIS 



425 



matter was produced and that of this green matter, with plants in moist 

 air, a large percentage occurred in the roots. In this, the aerial parts were 

 richer in water. It was determined in regard to the functions, that evap- 

 oration in moist air is absolutely less ; it is less also, however, per gram of 

 green and dry matter produced, i. e. the plant in the production of one gram 

 of material in moist air needs less water and this might occur because, 

 under these circumstances, it produces it Avith few mineral substances. 



A further experiment with peas' shows that the newly produced sub- 

 stance has an actually lower percentage of ash. The increased amount of 

 water taken up by the plant, because of the strong evaporation in dry air, 

 results in the plant's taking up in a given unit of time only half as con- 

 centrated a solution as it does with a weakened evaporation, when growing 

 in moist air. 



These results explain sufficiently why plants in moist air frequently 

 succumb more easily to disease than plants grown in dry air. The plants 

 are weaker in growth, richer in water and poorer in ash. Nevertheless, we 

 have no insight into the di\ ersity of the organic elements in the plant body. 

 It is very probable that plants grown in moist air are richer in sugar, 

 poorer in starch, as well as richer in asparagin and poorer in actual protein. 



Influence of Moist Air on Plants Injured by Drought. 



It has been supposed that plants which have suffered from intense 

 drought can be most cjuickly restored to their former activity if placed in 

 a very moist atmosphere. The following experiment shows the danger of 

 this procedure. Cherry seedlings, which survived a long drought in sand 

 cultures, at once showed an adjustment to the lessened amount of water 

 supplied the roots. At first, without change of habit of growth, evaporation 

 gradually decreased until the sand still contained possibly only 4 per cent, 

 of the amount held when saturated. At this point the plants began to wilt, 

 but, at the same time, evaporation ceased almost entirely. For example, 

 at a temperature of 30°C. and abundant sunlight, a little plant which had 

 formerly used daily about 8 g. water, evaporated only one decigram. After 

 adding considerable water, the plant gradually increased the amount of 

 evaporation. If, on the other hand, the drought continued too long, the 

 leaves dried backw'ard beginning at the tips, showing no discoloration. 



If now, after being wattered, the plants were brought into moist air 

 they did not recover as I had thought they would at first. Those under 

 the bell jars containing dry air had elevated the upper mature leaves, and 

 the partially dried bases of the older leaves became turgid again ; evapor- 

 ation again set in slowly. 



The gardener will find this observation of practical use in growing 

 potted plants. Excessively dry plants after watering must not be changed 

 in position. They must be somewhat shaded and they should not be placed 

 in air practically saturated with moistm-e, since this will stoj) almost all 

 activity. 



1 Loc. cit. p. 79. 



