PROTOPLASM MOVEMENTS. H 



free to move in any direction, while in tlie former its moye- 

 ments are greatly restricted by the surrounding walls. In 

 closed cells there are two general kinds of movements — one 

 a streaming, the other a mass movement — comparable to the 

 streaming and Amceba movements of the naked cells or pro- 

 toplasmic masses. No movement takes place, however (at any 

 rate to no great extent), until the vacuoles are quite large. 



12 — The streaming movements occur in the protoplasmic 

 strings, bands, and plates which cross or separate the vacu- 

 oles, and in the lining layer of protoplasm which invests the 

 inner surface of the cell-wall. The motion, in many cases, 

 shows the same alternation as in the Myxomycetes, the direc- 

 tion of the streaming usually being reversed after the lapse 

 of a few minutes. 



The mass-movement in closed cells is not as clearly sepa- 

 rated from the streaming as in naked cells. It usually con- 

 sists in a sliding or gliding of the protoplasm upon the inner 

 surface of the cell-wall, in much the same way as the naked 

 Plasmodium of one of the Myxomycetes moves upon the sur- 

 face of its supi^ort. The limited space in which its move- 

 ment must take place in closed cells, and its disposition over 

 the whole inner surface of the wall, compel the protoplasm 

 to move in opposite directions upon ojjposite sides of the 

 cell. There is thus a kind of rotation of the protoplasm 

 when the movement of all its parts is uniform. 



{a) The streaming movements may be studied in the stamen-hairs of 

 Tradeseantia Virginica, the stinging hairs of the nettle ( Urtica), the 

 hairs of Oucurbita, Eebalium, and Solanvm tuberosum, tlio styles of 

 Zea mais, the easily separated cells of the ripe fruit of Symplionoar- 

 pus racemoam, the young pollen grains of CEmthera, and the paren- 

 chyma of succulent raouocotyledons — e.g., in the flower peduncles and 

 the filaments of Tradescantia. The parenchyma cells of the leaves of 

 many trees and of the protliallia of ferns and Equisetums show a net- 

 work of hyaline strings in which a streaming may with difficulty be seen. 



Among the lower plants good examples may lie found in the hyphse 

 of some Saprolegni^, and in the cells of Spirogyra, Glosterium, Denti- 

 eella, and Ooscinodiscus. 



(b) In many cases (e.g., in the unfertilized embryo-sac of many 

 Phanerogams, in the young endosperm cells, and in the spore-mother- 

 cells of Anthoceros teTOs)— where the strings and bands resemble those 

 in the cases cited above— no movement of the jirotoplasm is visible, 



