134 PHYSIOLOGY OF NUTRITIO:N T . 



53. The Effect of Desiccation on Plant Structures. 



If cabbage sprouts are cut and kept without water, they soon 

 wither. If the process has gone far, we cannot bring the shoots 

 back to their normal condition by supplying them with water ; 

 but shoots which have just begun to wither, will often revive 

 again if plentifully supplied with water. 



To familiarise ourselves with the effect of desiccation on seeds 

 and seedlings, we employ wheat or pea seeds. Part of the 

 material is soaked for twenty-four hours in water, and then at 

 once placed in glass dishes and left exposed to the air to dry. The 

 rest is similarly exposed to the drying influence of the air when 

 the rootlets have just emerged, or have more or less developed. 

 When the seeds and seedlings have become air dry, we lay them 

 in moist sawdust, and observe their behaviour. The soaked 

 seeds have suffered little, and this is also the case with the seed- 

 lings whose roots have only developed to a very small extent. 

 The influence of the desiccation on somewhat further advanced 

 seedlings is shown in the death of the young parts; but on 

 renewal of the water supply these are replaced by the formation 

 of adventitious roots and the development of previously existing 

 axillary buds. Still more advanced seedlings usually perish 

 completely. 1 



If clumps of Barbula muralis are dried for several weeks in 

 the air, or over Sulphuric acid in a desiccator, and then moistened 

 and placed on moist earth, they go on growing again without 

 losing the old leaves. Many other mosses behave in a similar 

 manner, but others prove to be very sensitive to desiccation. 2 



I conducted a series of observations to determine how seedlings, 

 more or less dried, but still fairly rich in water, behave as regards 

 energy of respiration, as compared with normal ones. 3 About thirty 

 pea seedlings were examined with respect to their respiration 

 in the manner indicated in the Third Section. The amount of 

 Carbon dioxide expired by the seedlings in two to three hours at 

 a constant temperature is determined. Then they are deprived 

 of water for some days, and the more or less dried material is 

 again examined at the same temperature as before. Its respiratory 

 energy is .found to have fallen considerably. My observations 

 show that air-dry seeds do not give off a recognisable quantity 

 of Carbon dioxide. 



