HEALTH AND DISEASE. 95 



" elaborated sap " with the cambium, the formative 

 tissue which has to be fed and served by them, 

 and which by its growth suppHes new vessels and 

 sieve-tubes, etc., to carry the continually increasing 

 quantities of water and food substances as the 

 roots and leaves increase in number and area, and 

 thus enables this ideally correlated system to go 

 on working at maximum energy. 



Now suppose the same plant with its roots in 

 an unsuitable soil too dry or too poor in mineral 

 supplies, for instance- the transpiring leaves above 

 cannot obtain sufficient water and salts to supply 

 their needs, but we will suppose hypothetically 

 that they still assimilate under the same ideal 

 conditions as before. The supplies now coming 

 to the cambium are diminished, since the want of 

 water and minerals compels the leaves to put aside 

 any excess of carbohydrates {e.g. as stored starch- 

 grains), and the plastic materials which do pass to 

 the cambium so deficient in water cannot be directly 

 utilised, and a starvation period sets in. Con- 

 sequently the cambium forms less wood, and this 

 will contain fewer and smaller vessels, and so reduce 

 the conducting passages : fewer sieve-tubes also are 

 constructed, and the paths of the water current 

 and food supplies narrowed, which of course reacts 

 on the tissues everywhere. The reserve substances 

 may slowly be dissolved and distributed, however, 

 and considerable quantities be passed in course of 

 time into the roots, which, as opportunity offers, 

 gradually employ them in making new roots, and 

 if the disturbance has not gone too far and the 



