X PREFACE. 



gradients there is a small proportion of 

 sugar in solution. So long as a certain 

 temperature is maintained, with only a 

 given density of soil, air and heat will be 

 supplied to the stalks in such proportion 

 that the plant remains in health, and its 

 growth is unimpeded. In this case the 

 only change from a state of Nature is that 

 the green coloring matter is not elabo- 

 rated, and the stalk grows white. But 

 once pass this point and what is the re- 

 sult ? Shut out from air and light, sodden 

 with earthy water in which it is forced 

 to grow, the stalk becomes unhealthy, its 

 sugar changes to acid, the woody tissues 

 are burned or rusted, decay and then 

 decomposition ensues. In other words, 

 there is a certain definite quantity of air 

 and light required by a celery plant to 



