418 PHYSIOLOGY OF GROWTH. 



disappear, or new strands originate, and so forth. Excellent 

 objects for the study of the circulation of protoplasm are staminal 

 hairs of Tradescantia (e.g. T. virginica) taken from opening 

 flowers, and examined in a drop of water under the cover-glass, 

 as also are the hairs of the young shoots of Cucurbita Pepo. 



In the hairs of Tradescantia, Cucurbita, etc., primary proto- 

 plasmic movement is exhibited, i.e. the circulation takes place in 

 perfectly intact cells, and can hence be at once observed immedi- 

 ately after setting up the preparation. In the leaf-cells of Elodea 

 (we select examples in which we can see the bauds well, and in 

 which not too many chlorophyll grains are present on the near 

 walls), immediately after the leaves have been cut off, the move- 

 ment is only feeble, and often only to be observed with difficulty. 

 Gradually, e.g. after half an hour or an hour, it becomes more 

 vigorous, and then even tears away many of the chlorophyll 

 grains. 



Very generally, in perfectly intact plant-cells, the protoplasm 

 appears at rest ; the movement only takes place as the result of 

 stimuli due to the injuries which are unavoidable in making the 

 preparations. If we remove strips of epidermis from maize 

 plants cm. in height, and examine them as is best in 4 p. c. 

 cane-sugar solution (in order to avoid the injurious effect of the 

 water), we perceive no protoplasmic movement. Movement is 

 not clearly observable till after a quarter or half an hour. Here, 

 then, as in very many other cases, the primary protoplasmic 

 movement is entirely wanting. The secondary movement which 

 sets in is the result of injury. 1 



As to the causes underlying protoplasmic moments little is yet 

 known. In any case, however, when protoplasmic movements 

 are exhibited, a whole series of different processes are concerned, 

 and in different cases perhaps the chemical and physical antece- 

 dents are not always the same. Berthold 2 has attempted to 

 make the different forms of movement in protoplasmic masses 

 intelligible by reference to the movements exhibited under certain 

 conditions by dead particles. 



It is instructive to prove that inanimate substances are often 

 capable of movements which bear a certain resemblance to proto- 

 plasmic movements, a fact which, with many other circumstances, 

 must undoubtedly receive consideration in founding a future 

 theory of protoplasmic movements. 



On a dry sheet of glass, resting on white paper, we place with 



