290 DISEASE IN PLANTS. 



regards profundity, permanence, kind, etc., may- 

 well be imagined ; and there is nothing surprising 

 in our being able to induce them more easily 

 by the action of external factors in the readily 

 accessible cell-protoplasm than in the less exposed 

 nuclear-protoplasm ; because the latter is only 

 accessible through the former, or through the 

 agency of otJier nuclear protoplasm already modified. 

 On these and similar phenomena depend the 

 relative permanency and transmissibility of the 

 variations. Our measure of the latter only begins 

 when the effects referred to have become manifest 

 in large masses of cells, because only then do 

 they become appreciable to our senses. 



Further, variations thus induced may be of 

 advantage to the continued life of the plant, or 

 in all degrees disadvantageous or threatening to 

 its existence. These latter variations are Disease, 

 and if their interference with the normal rhyth- 

 mical play of the building up and breaking down 

 of the protoplasm molecules proceeds beyond 

 certain limits, life ceases, and we have death 

 supervening on disease. 



Notes to Chapter XXX. 



It appears prolDable that calcium is not always needed by 

 living cells, and may not enter into the composition of 

 protoplasm ; on the other hand traces of iron are perhaps 

 necessary. 



The criticisms and summary of facts on which the hypo- 

 thesis regarding protoplasm here adopted is based are 

 developed at length in Kassowitz, Allgemcijtc Biologic, 



