PROTOPLASM MOYEMWNTS. 13 



however, more or less parallel with the longer axis of the cell (Fig. 7). 

 In a string tliere may be one, two, or three currents ; when there are 

 two they are in opposite directions ; when there are three the central 

 one taljes one direction and the two outer ones the other. 



The strings are not stationary in the cell, but, on the contrary, they 

 change their position with a considerable rapidity, and in a prepara- 

 tion soon pass out of the focus of the microscope.* By this change of 

 place two strings may come together and fuse into one, or a string may 

 pass to the side of the cell and become obliterated by fusing with tlie 

 protoplasmic sac. New strings may be formed by a process exactly 

 opposite to the one j ust described. A stream in the substance of the 

 lining protoplasm forms a ridge projecting into the vacuole ; this ridge 

 gradually becomes higher, and finally breaks away from the protoplas- 

 mic sac, retaining its connection only at the ends. After a stream has 

 been running in a certain direction for from ten to fifteen minutes, the 

 motion suddenly becomes slower and soon stops entirely for from a few 

 seconds to several minutes, and then begins to move in the opposite 

 direction. The new movement begins and spreads as in the Myxomy- 

 cetes (see paragraph 7). 



{d ) In the hairs of Gueurbita Pepo the arrangement of the protoplasm 

 is much as in Tradescantia. The strings and bands are, however, 

 broader, and frequently contain several currents, and the nucleus, 

 instead of being imbedded in the lining layer of protoplasm, is in 

 a centrally placed mass. There is a more rapid change in tlie form 

 and position of the bands and strings than in Tradescantia, but the 

 streaming motion is, on the contrary, considerably slower. The reversal 

 of the streaming currents takes place in from seven to twenty minutes. 



(e) In most cases the streams lie in the lining protoplasmic layer of 

 the cell, or form low ridges upon its inner surface. This is the case 

 in the hairs of the style of Campanula, in hyphae (of fungi), and in the 

 suspensor and young embryo of Vurilda cmrulea. In long cells, the 

 movement being parallel with the longer axis, there may be, as in the 

 pollen tube of Zostera •marina, currents passing up one side and down 

 the other. ■]- 



* This fact must be borne in mind in studying the movements of pro- 

 toplasm in tliese cells, otherwise grave mistakes may be made. One 

 string may move out of focus, and another, with a contrary current, 

 may move into it, and thus a reversal of the current in tlie first string 

 may erroneously be supposed to have taken place. 



f To study the movements of protoplasm in pollen tubes it is usuaEy 

 necessary only to make a thin longitudinal slice of the stigma, and to 

 mount and cover it in the usual way, using no water, however. After 

 placing it under the microscope the preparation should be carefully 

 crushed, when some of the pollen tubes may be distinctly seen. Their 

 movements frequently continue for some hours in such preparations- 



