X1TELLA. 245 



by a still more remarkable structure of the sexual organs. They 

 are found not at all uncommonly growing at the bottom of ponds 

 and streams, and in bog holes, forming long dense tufts of green 

 thread-like stems, rooted in the mud by means of delicate hairs, 

 or rhizoids. The Stone worts are divided into two genera, Nitella 

 and Chara, distinguished for our present purpose by differences 

 in the structure of the stem. As the more simply organised, we 

 may commence our study with Nitella. The slender axis, exam- 

 ined with the naked eye, is seen to be segmented; long bare 

 segments alternating with whorls of appendages. The former 

 are the internodes, the latter arise from the nodes. We have 

 here therefore an apparent approach to the condition of affairs 

 met with in the flowering plants already studied. Each internode 

 consists of a single very elongated cylindrical cell. The principal 

 characteristics of this internodal cell we have already examined 

 (see p. 50). It possesses a firm, well-developed, transparent cell- 

 wall ; underlying this is a lining layer of protoplasm, in which 

 are embedded innumerable regularly-arranged "chlorophyll bodies, 

 with thin layers of protoplasm between them. Inside the 

 stationary layer is a layer of protoplasm in the active streaming 

 movement known as rotation, The general cavity of the cell is 

 filled with cell-sap. The neutral lines will be readily visible ; 

 these, and the lines of chlorophyll bodies, pass spirally along the 

 cell. The node consists of a single disk-like cell, on the edges of 

 which are borne appendages (" leaves," or " branches''), likewise 

 consisting each of a thread of cells. From the lowermost nodes 

 arise long, often branched rhizoids, divided by oblique partition 

 walls. As we pass higher up the stem the internodes become 

 progressively shorter, and the nodes and their appendages there- 

 fore nearer together, until at the summit they are crowded 

 together into a terminal bud. 



Dissect out this bud under the microscope by means of needles. 

 This is best done from material laid for from twelve to twenty-four 

 hours in a 1 per cent, watery solution of chromic acid. The bud is 

 laid upon a slide, and with needles the lowest portions are suc- 

 cessively removed so long as it appears safe to do so. These 

 portions are then removed out of the way, a small drop of glyce- 

 rine added to the specimen, the cover-glass laid on, and by gentle 

 pressure with the needles upon the cover-glass, while observing 

 through the microscope, the bud slightly crushed. It is probable 

 that the bud will open, and disclose its structure. At the apex 



