274 DISEASE IN PLANTS. 



invisible and intricate meshwork, bathed in a 

 watery liquid held in the interstices somewhat as 

 water is held in a sponge. In this imbibed 

 liquid are dissolved the substances, consisting of 

 the same elements, which are to serve as food, 

 and which are to be taken up into the molecular 

 framework and built up into the structure of 

 new molecular units or, as they may be shortly 

 termed, molecules of protoplasm : in the bathing 

 liquid are also dispersed the fragments again con- 

 taining the elements named which have resulted 

 from the breaking asunder of some of the complex 

 protoplasm molecules, and which are partly de- 

 stined to be used up again, partly to be burnt 

 off in respiration, and partly to be put aside as 

 metabolic products such as reserves, secretions, 

 permanent structure, etc. Among the elements 

 carried into this liquid and dissolved in it the free 

 oxygen of the air also plays an important part. 



As new molecules are formed, by mutual 

 combinations of the food-materials selected by 

 molecular attractions, they are taken up into the 

 protoplasmic framework, and built in between 

 those already in existence, thus distending the 

 whole, and we say that the protoplasm Assiniilates 

 food-materials and Grows. When distended 

 beyond a given degree, or disturbed in various 

 other ways, the molecular framework breaks, and 

 some of the molecules are shattered, and as they 

 fall to pieces certain of their constituent parts 

 containing carbon and hydrogen forcibly combine 

 at the moment of liberation with the oxygen in 



