PROTOPLASM MOVEMENTS. 11 



free to move in any direction, while in the former its move- 

 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 Amoeba 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 usuallv con- 



O */ . 



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 

 plasniodium of one of the Myxomycetes moves upon the sur- 

 face of its support. 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 opposite 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 

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

 liairs of Cucurbita, Ecbalium, and Solarium, tuberosum, the styles of 

 %ea mats, the easily separated cells of the ripe fruit of Symphoncar- 

 pus racemosus, the young pollen grains of (En.othera, and the paren- 

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

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

 many trees and of the prothallia 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 be found in the hyphae 

 of some Saprolegnise, and in the cells of Spirogyra, Closterium, Denti- 

 cella, and Coscinodiscus. 



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

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

 cells of Anthoceros Icevis) where the strings and bands resemble those 

 in the cases cited above no movement of the protoplasm is visible, 



