51 



Pitfiiilly it is equally unjustifiable to deduce from con- 

 ditions under which certain tissue formations cannot devel- 

 op conculsions as to the functions which they would have 

 performed under normal conditions. Tissues not developed 

 m cultures in moist air are not thereby justified as ar- 

 rangements to provide against too high transpiration. V/e 

 come nearer the truth indeed through the assumption that 

 plants m moist cultures, etc. "cannot" develop definite 

 tissue forms, than hy the supposition that the plant no 

 longer develops these forms, because the^ are "no longer 

 necesaary" to it. 



Taken all in all, the tissue hypoplasias as yet known, 

 do not seem to me suitable to prove the capacity of the 

 plant for a self-regulating adjustment to unfavorable ex- 

 ternal conditions. 



We have already spoken repeatedly of the factors by 

 which hypoplasiaa are produced. If we glance once more over 

 the facts at hand, v;e can verify the statement that almost 

 all of the described hypoplasias may be traced back to 

 scanty nourishment . It is hence evident that the plants 

 Ijegetating in disfilled water and those cultivated in the 

 dark or without carbon dioxid, in which we have ascertained 

 hypoplasias, are more poorly nourished than normal ones, 

 Hov/ever, the same holds good also for the individuals which 

 have been grown in moist places or under water, v/hich at 

 once, with a normal degree of transpiration, lose the supply 

 of fooS substance v/hich is necessary for normal tissue 

 formations. 



It becomes evident, especially in the higher plants, 

 that, with insufficient nourishment, not only certain pro- 

 cesses of grovi/th, formation, and differentiation become im- 

 possible, but that usually a large number of varied pro- 

 cesses also are lacking. Arrestment in the differentiation 

 of the tissues makes itself evident not only in one tissue 

 form of an organ, but usually in several, often in all. Only 

 when the injurious influences are moderately effective do 

 we occasionally find that the development of the "more sus- 

 ceptible" tissue forms, such as, for example, the ducts, is 

 influenced, and that the development of those more resistant, 

 for example, the epidermis, comes to maturity unchanged, 

 (53) According to our present knowledge, there are no factors 

 which even when acting energetically, influence only one 

 tissue form, and thus prevent normal development. 



The discussion of this point seemed necessary 

 in viev/ of the contents of t later chapter. We v/ill 

 see later thai, by increased utilization, ^he forma- 

 tion of individual tissues of the plant can be en- 

 couraged, while the development of others, on vti ich 

 no increased demands are made, does not exceed the 

 normal amount. It would be conceivable that, as 

 a result of abnormally weak demand upon them, those 

 tissues forms, of which less is required, ?;ould re- 

 main below the normal in their development while the 



