PROTOPLASM AND LIFE. 731 



to bear on one of these cells, a portion of its protoplasm may be seen 

 in active rotation, flowing up one side of the long, tubular cell and 

 down the other, and sweeping on with it such more solid particles as 

 may become enveloped in its current. In another water-plant, the 

 Vallsnerla spiralis, a similar active rotation of the protoplasm may 

 be seen in the cells of the leaf, where the continuous stream of liquid 

 protoplasm sweeping along the green granules of chlorophyl, and 

 even carrying the globular nucleus with it in its current, presents one 

 of the most beautiful of the many beautiful phenomena which the mi- 

 croscope has revealed to us. 



In many other cells with large sap-cavities, such as those which 

 form the stinging hairs of nettles and other kinds of vegetable hairs, 

 the protoplasmic lining of the wall may send off into the sap-cavity 

 projecting ridges and strings, forming an irregular network, along 

 which, under a high power of the microscope, a slow streaming of 

 granules may be witnessed. The form and position of this protoplas- 

 mic network undergo constant changes, and the analogy with the 

 changes of form in an Amoeba becomes obvious. The external wall 

 of cellulose renders it impossible for the confined protoplasm to emit, 

 like a naked Amoeba, pseudoppdia from its outer side ; but on the 

 inner side there is no obstacle to the extension of the protoplasm, and 

 here the cavity of the cell becomes more or less completely traversed 

 by protoplasmic projections from the wall. These often stretch them- 

 selves out in the form of thin filaments, which, meeting with a neigh- 

 boring one, become fused into it ; they show currents of granules 

 streaming along their length, and after a time become withdrawn and 

 disappear. The vegetable cell, in short, with its surrounding wall of 

 cellulose, is in all essential points a closely imprisoned rhizopod. 



Further proof that the imprisoned protoplasm has lost by its im- 

 prisonment none of its essential irritability, is afforded by the fact that 

 if the transparent cell of a Nitella, one of the simple water-plants just 

 referred to, be touched under the microscope with the point of a blunt 

 needle, its green protoplasm will be seen to recede, under the irritation 

 of the needle, from the cellulose wall. If the cellulose wall of the 

 comparatively large cell which forms the entire plant in a Vaucheria, 

 a unicellular alga .very common in shallow ditches, be ruptured under 

 the microscope, its protoplasm will escape, and may then be often seen 

 to throw out pseudopodial projections and exhibit amoeboid move- 

 ments. 



Even in the higher plants, without adducing such obvious and well- 

 known instances as those of the sensitive-plant and Venus's flytrap, 

 the irritability of the protoplasm may be easily rendered manifest. 

 There are many herbaceous plants, in which, if the young, succulent 

 stem of a vigorously growing specimen receive a sharp blow, of such 

 a nature, however, as not to bruise its tissues, or in any way wound it, 

 the blow will sometimes be immediately followed by a drooping of the 



