540 TRANSFORMATION OF ENERGY 



when oxygen is absent from the environment. Whether or not organisms like 

 Thiothrix must be added to this category appears doubtful (Wille, 1902). 



• . Since the dependence of movement on oxygen is so variable, it is needless 

 for us to attempt the determination of the limits of partial pressure of oxygen 

 permissive of movements in relation to individual organisms ; it is manifest 

 at once that each organism must have an optimum, a maximum, and minimum 

 (Clark, 1888). 



The influence of temperature is very striking and many estimates have 

 been made on the subject. The rate of rotation under different temperatures 

 has been accurately studied more especially. The following table, based on the 

 observations of Velten on the leaves of Vallisneria and condensed by Schafer 

 (1898) will illustrate this : — 



It may be clearly seen that the rate of movement increases at first rapidly 

 and then more slowly, until the optimum is reached at 31°, and that, thereafter, 

 it as rapidly falls ; above 35° C. heat rigor sets in. The minimum does not 

 always, as in this case, lie somewhere near zero ; in many terrestrial plants it 

 obviously lies much higher. The optima and maxima also may be considerably 

 higher, e.g. 40° and 50°, or even above these temperatures (Hauptfleisch, 

 1892). The phenomena in this respect resemble those of growth, so that we 

 need not pursue the matter further. Similar results have been obtained from 

 the study of the motile swarmspores. 



As far as light is concerned, it may be briefly said that its influence on 

 locomotion is indirect only, inasmuch as many organs develop very imperfectly 

 or not at all in the dark and hence, naturally, protoplasmic movement does 

 not take place in them. Further we know that intense sunlight is fatal both 

 to ciliary and protoplasmic movement. If, however, swarmspores or cells ex- 

 hibiting streaming protoplasm, previously exposed to diffuse light, are placed 

 in the dark, the movements do not appear to suffer any change. 



•Recently Josing (1901) has made some remarkable observations on this 

 point. Protoplasmic streaming ceases at once in the dark when the cells are 

 treated with ether or chloroform, with carbon-dioxide or non-volatile organic 

 acids, or salts, but the movements continue in presence of these substances 

 if the cells be illuminated. The same author has recorded additional observa- 

 tions as to the action of ether not less remarkable, but he was unable to give a 

 causal explanation of them. 



Still less comprehensible is the well-established fact that protoplasmic 

 streaming may arise in cells which have been separated from the plant though 

 they show no such movements when incorporated in it (Keller, 1892). [Com- 

 pare Kretschmar, 1903.] In other cases an already existing protoplasmic 

 movement may be accelerated merely by wounding the cells. It is equally well 

 established that movement may occur in many cases where no injury whatever 

 has been inflicted (Hauptfleisch, 1892). De Vries (1885) has pointed out that 

 this streaming effectively aids in establishing a uniform distribution of materials 

 in the cell, and that, too, much more rapidly than by simple diffusion, so facili- 

 tating the circulation of nutrients, &c., in the plant. Since, however, proto- 

 plasmic movement is not so widespread in the uninjured plant as De Vries 

 assumed, obviously such a circulation must be effected without the aid of proto- 

 plasmic movement. The further services rendered by streaming, such as the 

 shifting of the position of chloroplasts, we shall treat of in our next lecture. It is 

 impossible at present to pronounce an opinion as to whether the movements which 

 follow after or are accelerated by wounding are to be considered as purposeful 



