SUPPLEMENT 81 



study leads us to the conclusion that the structural traits they have in common 

 are adaptations to their habitat. 



253, 11. 38-44, for These brief notes . . . from each other, read It is a well- 

 known fact that many plants can grow both on land and in water, and that they 

 develop very differently in these two situations ; as an illustration, we may 

 refer to the land and water forms of Polygonum amphibium. 



254, 11. 1-31, for Since it has been shown ... to the conclusion that every 

 change read Since then the water and the land forms are obviously organized 

 in relation to the media they inhabit, we have here to deal with adaptations, 

 or more correctly, self-adjustments, on the part of the plant ; these, however, 

 we cannot consider in greater detail at present. Just as in this case the adapta- 

 tion arises in consequence of the influence of one or more external factors, so in 

 other instances, which we will not speak of at present, a new and distinct func- 

 tion, differing from that ordinarily exhibited by the organ in question, may 

 make its appearance. 



What is of especial interest to us in all the phenomena referred to above, 

 is the fact that the plant body does not possess a predestined form fixed once 

 and for all, but that it is capable of modification, and it must be the task of 

 physiology to discover the causes of such transformations. In very many 

 cases it is possible to refer such changes to known external factors, while, in 

 other cases, we must look for their origin in causes which are internal, and with 

 which we have less acquaintance. It would, however, be quite incorrect to 

 suppose that the plant reacts purposefully to every alteration in the environ- 

 ment. In numberless instances the question whether the reaction which takes 

 place is purposeful or not depends very much on individual opinion. As far 

 as the physiologist is concerned, the question is, generally speaking, rather 

 a subsidiary one, for he deals only with the factors concerned in formation, 

 while the biologist is more concerned with problems as to its aim and object. 

 Since, then, a purposeful reaction on the part of the plant very frequently 

 cannot be denied, attempts have been made to see in this reaction something 

 especially characteristic of the organism, and the question has of recent years 

 been again put forward, with renewed interest, whether the phenomena of the 

 organic world (more especially those of metamorphosis) have their origin in 

 the same forces and obey the same laws as those of the inorganic world, or 

 whether we must assume in their case conditions of a quite special nature. In 

 order to decide between these alternatives, we must anticipate to some extent 

 the conclusions of the lectures to follow. We shall see that every change 

 (follow on to P. 256, 1. 29 plant physiology.]) 



256, 1. 30 P. 257, 1. 28, delete From the examples . . . external factors. 



258, 1. i, before The most simply, &c. insert In the second part of this 

 course of lectures we have to discuss the change in form in plants, to inquire 

 into the causes of growth, formation, and development. We have hitherto 

 regarded the formative processes as something taken for granted, and treated 

 ihem either only in a descriptive or comparative manner from the historical 

 or hereditary point of view ; but that it is possible to look at the subject causally 

 also is a conclusion arrived at in recent times by morphologists and physiologists 

 alike. SACHS, VOCHTING, GOEBEL, KLEBS, andBERTHOLD may be reckoned as 

 the founders of ' developmental physiology '. A comprehensive exposition of 

 this branch of our science is as yet non-existent, and hence the following attempt 

 cannot in any sense lay claim to completeness. Nevertheless we think that 

 by separating this subject from ' transformation of energy ' or ' physical physio- 



JOST F 



