12 REPORT— 1879. 



teresting group of simple plants, common in the clear water of ponds and 

 of slowly running streams. The cells of which they are built up are 

 comparatively large, and, like almost all vegetable cells, are each enclosed 

 in a wall of cellulose. The cellulose is perfectly transparent, and if the 

 microscope, even with a low power, be brought 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 Valisneria spiralis, a similar active rotation 

 of the protoplasm may be seen in the cells of the leaf, where the con- 

 tinuous stream of liquid protoplasm sweeping along the green granules of 

 chlorophyll, and even carrying the globular nucleus with it in its current, 

 presents one of the most beautiful of the many beautiful phenomena 

 which the microscope 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 pro- 

 toplasmic 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 protoplasmic 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, pseudopodia 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 com- 

 pletely traversed by protoplasmic projections from the wall. These often 

 stretch themselves out in the form of thin filaments, which, meeting with 

 a neighbouring 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 streaming along their length, and after a time become withdrawn and 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 com- 

 paratively 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 movements. 



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 how.* 



