THE AMERICAN WATER WEED. 127 
the while changing colour as the polarizing prism is revolved, 
a ever changing kaleidoscopic pictures of wonderful 
eauty. 
In no plant perhaps is the growing point (punctum vegeta- 
tionis) of the stem more easily prepared for study than in 
Anacharis. All that is necessary is to strip off the lower en- 
veloping leaves until the apex of the stem is exposed as a white 
point. Microscopical examination of this then reveals in an 
unusually clear manner the acropetal development of the leaves, 
and the long cone of small-celled protomeristem tissue which 
forms the growing point. See fig. 2; in which the youngest 
leaves appear as mere prominences of the meristem tissue 
above, and gradually grow into the normal form below; the 
older leaves, which had curved over and so protected the 
tender growing point, having been torn away below to expose 
poe the apex of the stem and the glands (fig. 2, g.) described 
below. 
The leaves are sessile, from 3 to }™ of an inch in length, 
oval to linear in form, acute and margined; and are arranged 
upon the stem in whorls of threes or fours above,—opposite 
below. As in all submerged aquatic plants, they are not covered 
with a distinct epidermis, nor are the superficial cells cuticular- 
ised. Consequently the cell walls are very transparent, permit- 
ting a clear view of their contents, and also of the phenomenon 
of cyclosis, which they show in a very high degree. The leaf 
border consists of a single layer of cells, the apices of some of 
which are produced into little teeth forming a distinctly serrated 
margin. Nearer the central rib the cells are two or three deep. 
The central rib itself consists of elongated cells, which, as already 
stated, are in direct connection with the central axis of the stem. 
(fig. 5 /.¢.) In Science Gossip for 1869, Mr. T. Smwpson gives 
the following particulars respecting the structure of the leaves of 
Anacharis :— 
Aaeraers Size. No. of Cells, Xo: 0f Chlorophyll No. of ditto 
Granules in each cell. in whole leaf. 
24 7 
12 Leaves =a x iio 9, 100 23 209,300 
6 Leaves ~ x = 9,750 22 214,500 
A rather high power is necessary to see the cyclosis to perfection, 
but it well repays the trouble of careful illumination and 
examination with a ;1," or =," inch objective, for in addition 
to the ordinary rotation round the interior of the cells of a dense 
layer of protoplasm in which the chlorophyll granules are carried, 
there is then also brought into view a network of exceedingly 
fine anastomosing threads of protoplasm which traverse the cell 
cavity in all directions. 
The great advantage of Anacharis leaves as a subject in which 
to observe eyclosis, is the fact that they need no slicing. A 
