158 TKANSACTIONS LIVEEPOOL BIOLOGICAL SOCIETY. 



why, of closely allied plants, the plasma of the one may be 

 capable of withstanding dessication, that of the other not, 

 the difference being due to the fact that the plasma of the 

 more resistant form has acquired, by adaptive modification, 

 the power of, when dessicated, re-arranging its molecules 

 in a stable form from which recovery is possible, whilst in 

 the other case the stable substance or rather substances 

 into which the protoplasmic molecule resolves on drying 

 are such that from them no re-constitution of the proto- 

 plasmic molecule is, inter se, possible. 



In plants which can withstand dessication very varied 

 degrees of resistance are shown. These differences are 

 probably due to the fact that the protoplasmic molecule 

 can, in some cases, retain the necessary molecular arrange- 

 ment which permits of re-organization for a very long 

 time, but in others, only for a limited period. Thus 

 seeds of Oxalis* Salix\ and Populus\ are killed by 

 from 1 to 3 weeks air drying, and in many cases the 

 duration of the drying is more important than its degree. 

 The presence of oil in the plasma does not seem to make 

 it more resistant to dessication, as Alex. Braun§ supposed, 

 for Hemp seeds are less resistant than Peas or Barley and 

 Dicranum scoparium is less resistant than Orthotrichum 

 affine or Bryum ccespititium. As Schroder (1. c.) points 

 out, however, when the oil is coloured (lipochrome pig- 

 ments, etc.) and present in microscopic organisms (many 

 Palmellacese, etc.) it may be of importance as a protection 

 against the decolourization which sunlight may induce in 

 dried cells containing chlorophyll. 



*F. Hildebrand. Uber die Schutzeinrichtungen der Oxaliszwiebeln. 

 Ber. d. D. Bot.-Gesell., 1884, Hft. 3. 



tWiclmra. Die Bastardbefruclitung der Weiden, 1865. 



J Schroder, L. c. Nobbe. Handbuch der Sanienkunde, 1876. 



§ Alex. Braun. Betraclitungen liber die Erscheinung der Verjungung in 

 der Natur, 1850. 



