Januaey 14, 1910] 



SCIENCE 



57 



great deal is unlmown there are a number 

 of important facts concerning whieli there 

 is positive information and which throw 

 considerable light on what is really taking 

 place under such conditions. It is best, be- 

 fore taking up the physiological reactions, 

 to consider the morphological changes 

 which ensue, which, if we wish to employ 

 modern terminology, we may term "chem- 

 omorphosis." The information regarding 

 the lower forms— particularly the fungi 

 —is the fullest and will be considered 

 first. 



The primal fact of the increase on dry 

 weight has already been spoken of and is 

 the simplest of all the reactions to demon- 

 strate. By the easy process of the desicca- 

 tion and weighing of a series of cultures 

 the stimulation curve of the whole range 

 of possible concentrations from minimum 

 to maximum may be determined. Although 

 it must be said that to obtain definite re- 

 sults means which might seem to some to 

 be exaggeratedly careful must be taken to 

 ensure the purity of all substances entering 

 into the culture medium. Not only is the 

 quantity of mycelium formed greater, but 

 also the form and appearance are very dif- 

 ferent. Fungi commonly cease to form 

 conidia under stimulation, the mycelial 

 felts are buckled and knotted instead of 

 being flat and even and their consistency 

 is different, being tough and leathery in- 

 stead of somewhat tenuous in texture as in 

 the normal growth. In short they present 

 every appearance of more luxuriant vege- 

 tative activity. The cell forms are often 

 different, especially among bacteria, where 

 the so-called involution forms arise appar- 

 ently from chemical stimulation. Among 

 many of the fungi, at least, such conditions 

 are tantamount to a state of hyperplasia, 

 if we may use the term in speaking of such 

 lowly organized forms. Among the higher 

 plants there may be simply an increased 



rate of growth and an ultimately greater 

 stature, or, in other cases, as in the local 

 application of metallic salts in initiating 

 local intumescences or in hastening and in- 

 creasing the formation of wound tissue, 

 actual hypertrophies may be induced. In 

 the stimulation afforded by parasitic fungi 

 or by gall insects the great expression of 

 abnormal growth is to be seen amounting 

 often to relatively large outgrowths of 

 tissue. The reaction in these various cases 

 would seem to differ rather in degree than 

 in kind, and it is perhaps a question not in 

 this case of a mere hastening of growth, but 

 of the excitation being sufficiently violent 

 to destroy the equilibrium of growth which 

 exists among the cells. 



In no such case, however, have we any 

 evidence that the variations in form so in- 

 duced are inheritable. It is only when the 

 germ cells at or near the time of their for- 

 mation are directly stimulated that we get 

 any changes in the offspring which are 

 passed on to the succeeding generations. 

 Sometime, it may be, means will be found 

 by which an excitation of the sporophyte 

 can be made in some way to influence the 

 gametophytic cells and thus induce perma- 

 nent variations through influences brought 

 to bear indirectly upon the gametophyte, 

 though it is not to be supposed even in that 

 ease that the particular response induced 

 in the original sporophyte will be repeated 

 in its offspring. 



It is evident, from the effect of parasitic 

 fungi upon their hosts, that not only does- 

 the stimulus of the parasitism of a specific 

 fungus produce more or less specific re- 

 sults, but also that the condition of the' 

 parasitized cells themselves influence the- 

 result. The more primitive or meristem- 

 atie are the cells the greater the result- 

 ant effect in the way of a distortion, for,, 

 as is well known, the greatest hypertro- 

 phies take place when the infection! is. in: the 



