RELATIONS OF PKOTOPLASM TO GRAVITATION. 209 



nij-eetes to become rounded into the form of somewhat flattened 

 drops, from which slender branches protrude after a short time. 

 If pressure is novv made upon those portions of tlie branched 

 Plasmodium in which circulation is to be seen, the movement 

 stops at onoe, and is not resumed for two or three minutes ; 

 but after that period of rest it goes on as before. When a 

 Plasmodium is cut in halves, tlie circulation is to be seen after 

 a while in the separated portions.^ 



577. Eelations of protoplasm to gravitation. Concerning the 

 influence of gravitation on the form assumed by protoplasm, it 

 need only be said here that the less dense plasraodia appear some- 

 times to yield to this force. But Pfeff'er ^ found that in a saturated 

 atmosphere the plasmodium of -32thalium moved in the dark with 

 equal freedom whether the moist bibulous paper on which it rested 

 was held horizontally' or verticall}- ; Sti-asburger ' also has noted 

 the same fact. If one part of the paper is more moist than an- 

 other, it is to the very wet spot that the plasmodium wanders. 



578. Belafcions of protoplasm to moisture. The relations of 

 water to the activity of protoplasm are not j'et thoroughly under- 

 stood. It has been seen (577) that there is a tendency of Plas- 

 modia to move to the points where there is the most moisture ; 

 and in general it may be said that a large amount of water is 

 favorable to all protoplasmic movements. Thus Dehneeke ' 

 found that the protoplasm in the cells of the collenchj-ma of 

 Balsamina exhibited no circulation until the section had been 

 placed in water ; and the same phenomena can be shown in 

 sections of many active plants. 



On the other hand, Velten has shown that in some cases the 

 protoplasmic movement stops when a plant-hair is placed or kept 

 for a time in water, but is resumed if it is transferred to a dilute 

 solution of gum-arabic, although the protoplasm was furnished 

 with a greater supply of water in the former than in the latter 

 case. 



579. Some harmless plasmolytic agents (see p. 27), for in- 

 stance a dilute solution of sugar, added to the water in which the 



1 Pfeffer : Pflanzenphysiologie, 11. 390. 



2 Pfeffer : Pflanzenphysiologie, ii. 388. 



5 Wirkung des Liclites auf Schwarmsporen, 1878, p. 71. Dehneeke (Uebev 

 nicht assimilirende Chlorophyllkbrper, 1880) has shown that the various 

 bodies which occur in protoplasm of cells — for instance, chlorophyll granules, 

 starch-grains, and the like — have a marked tendency to sink to that part of 

 the cellulose wall which is lowest. The change of position takes place some- 

 times in a few minutes, sometimes only after several hours. 



* Flora. 1881, p. 8. 



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