ROTATION IN VALLISNERIA AND ANACHARIS. 363 



in the Nuphar lutea (Yellow water-lily), the footstalks of whose 

 leaves contain large air-chambers, the walls of which are built 

 up of very regular cubical cells, whilst some curiously formed 

 large stellate cells project into the cavity which they bound (Fig. 

 152). The dimensions of the component vesicles of Cellular 

 tissue are extremely variable ; for although their diameter is very 

 commonly between l-300th and l-500th of an inch, they occa- 

 sionally measure as much as l-30th of an inch across, whilst in 

 other instances they are not more than l-3000th. 



224. The component cells of Cellular tissue are usually held 

 together by an intercellular substance, which may be considered 

 analogous to the " gelatinous" layer that intervenes between the 

 cells of the Algae. There are many cellular substances, how- 

 ever, in which, in consequence of the loose aggregation of their 

 component cells, these may be readily isolated, so as to be pre- 

 pared for separate examination without the use of reagents 

 which alter their condition; this is the case with the pulp of 

 ripe fruits, such as the Strawberry or Currant (the Snowberry is 

 a particularly favorable subject for this kind of examination), 

 and with the parenchyma of many fleshy leaves, such as those 

 of the Carnation (Dianthus caryophyllus) or the London Pride 

 [Saxifragra erassifolia). Such cells usually contain evident 

 nuclei, which are turned brownish-yellow by iodine, whilst their 

 membrane is only turned pale-yellow; and in this way the 

 nucleus may be brought into view, when, as often happens, it is 

 not previously distinguishable. If a drop of the iodized solution 

 of chloride of zinc be subsequently added, the cell-membrane 

 becomes of a beautiful blue color, whilst the nucleus and the 

 granular protoplasm that surrounds it, retain their brownish- 

 yellow tint. The use of dilute nitric or sulphuric acid, of alco- 

 hol, of syrup, or of several other reagents, serves to bring into 

 view the "primordial utricle" of Mohl; its contents being made 

 to coagulate and shrink, so that it detaches itself from the cellu- 

 lose wall with which it is ordinarily in contact, and shrivels up 

 within its cavity, as shown in Fig. 149. 



225. It is probable that all cells, at some stage or other of their 

 growth, exhibit, in a greater or less degree of intensity, that 

 curious movement of "rotation," which has been already de- 

 scribed as occurring in the Gharacce (§ 201), and which consists 

 in the steady flow of one or of several currents of protoplasm 

 over the inner wall of the cell ; this being rendered apparent by 

 the movement of the particles which the current carries along 

 with it. _ The best examples of it are found among submerged 

 plants, in the cells of which it continues for a much longer 

 period than it usually does elsewhere ; and among these there 

 are two, the Vallisneria spiralis and the Anacharis alsinastrum, 

 which are peculiarly fltted for the exhibition of this interesting 

 phenomenon. The former is an aquatic plant that grows abun- 

 dantly in the rivers of the south of Europe, but is not a native 



