46 PHYSIOLOGICAL MORPHOLOGY 



a movement corresponding to the new conditions of equilibrium has had 

 time to take place, equilibrium may be again altered and a corresponding 

 change in the movement induced. In accordance with this is the fact 

 that free protoplasts or myxomycete plasmodia having a definite shape 

 tend to assume a rounded and globular form when either their vitality 

 or their powers of movement are depressed. The vacuolar structure, which 

 Blitschli considers protoplasm to possess, will certainly be influenced by, 

 and be the direct result of the same general tendency l . 



It is impossible at present to say what factors and mechanical agencies 

 operate in inducing all the different processes and changes of form of which 

 protoplasm is capable, though it is safe to assume that these are mainly 

 due to local or general chemical actions, and the changes of surface 

 tension, &c. which result from and accompany them. The power which 

 protoplasm has of retaining the same general structure, in spite of the 

 perpetuai, changes going on within it, is as yet an unsolved problem, as 

 well as is the reason for the tendency to reject and expel foreign bodies - 

 which it possesses. 



The results observed do not form any direct indication of the inducing 

 causes which are at work. Thus it is both illogical and unmethodical to 

 suppose that in the visible formative changes which accompany mitotic cell- 

 division we see the actual internal causes by which cell-division is induced, 

 and for the same reason it is just as impossible to decide which parts are 

 active and which passive. (Cf. Chap. I.) The translocatory movements 

 and general behaviour of dissolved and undissolved excretory or plastic 

 substances, constantly found in the plasma though not essentially part of it, 

 are of considerable physiological interest. Such substances, or the plastic 

 material alone, may be termed food material (Hertwig, Zelle, p. 24) 

 metaplasia 3 , paraplasm (Kupfer), or deutoplasm (van Beneden). It is, 

 however, not always easy to clearly distinguish between plastic substances 

 and excrete products. 



SECTION 8. The Origin of Plasmatic Organs. 



In order that hereditary characteristics may be successively trans- 

 mitted from one generation to another, it is necessary that not only the 

 protoplast, but also the elementary organs which the latter contains, should 

 be able to divide and reproduce their own kind. Thus, new nuclei and new 

 chromatophores are formed only by the division of pre-existent chromato- 



1 See Klemm, ' Desorganisalionserscheinungen,' Jahrb. f. wiss. Bot., Bd. xxvm, Heft 4, 1895, 

 p. 70. 



8 Pfeffer, Aufnahme und Ausgabe ungeloster Korper, 1890, p. 174. 

 ;; Hnnstein, Bot. Zeitung, iS68, p. 710. 



