690 MICROSCOPIC STRUCTURE OF PHANEROGAMIC PLANTS 



phenomenon may be most luxuriously watched under their patent 

 binocular. 



Anacharis alsinastrum is a water- weed which, having been acci- 

 dentally introduced into this country many years ago, has since 

 spread itself with such rapidity through our canals and rivers as in 

 many instances seriously to impede their navigation. It does not 

 require to root itself in the bottom, but floats in any part of the water 

 it inhabits ; and it is so tenacious of life that even small fragments 

 are sufficient for the origination of new plants. The leaves have no 

 distinct epiderm, but are for the most part composed of two layers of 

 cells, and these are elongated and colourless in the centre, forming a 

 kind of midrib ; towards the margins of the leaves, however, there is 

 but a single layer. Hence no preparation whatever is required for the 

 exhibition of this interesting phenomenon, all that is necessary being 

 to take a leaf from the stem (one of the older yellowish leaves being 

 preferable), and to place it, with a drop of water, either in the aqua- 

 tic box or on a slip of glass beneath a thin glass cover. A higher- 

 magnifying power is required, however, than that which suffices for 

 the examination of the cyclosis in Chara or in Vallisneria, the ^-iiich 

 object-glass being here preferable to the ^-inch, and the assist- 

 ance of the achromatic condenser being desirable. With this ampli- 

 fication the phenomenon may be best studied in the single layer of 

 marginal cells, although, when a lower power is used, it is most evi- 

 dent in the elongated cells forming the central portion of the leaf. 

 The number of chlorophyll-granules in each cell varies from three or 

 four to upwards of fifty ; they are somewhat irregular in shape, some 

 being nearly circular flattened discs, whilst others are oval ; and 

 they are usually from y^-^th to r^^th of an inch in diameter. 

 When the rotation is active the greater number of these granules 

 travel round the margin of the cells, a few, however, remaining fixed 

 in the centre ; their rate of movement, though only ^th of an inch 

 per minute, being sufficient to carry them several times round the 

 cell within that period. As in the case of Vallisneria, the motion 

 may frequently be observed to take place in opposite directions 

 in contiguous cells. The thickness of the layer of protoplasm in 

 which the granules are carried round is estimated by Mr. Wenham 

 at no more than ^ ^ 00 th of an inch. When high powers and 

 careful illumination are employed, delicate ripples may be seen in the 

 protoplasmic currents. 1 



Cyclosis, however, is by no means restricted to submerged plants ; 

 for it has been witnessed by numerous observers in so great a variety 

 of other species that it may fairly be presumed to be universal. It is 

 especially observable in the hairs of the epidermal surface. Such 

 hairs are furnished by various parts of plants ; and what is chiefly 

 necessary is that the part from which the hair is gathered should be 

 in a state of vigorous growth. The hairs should be detached by 

 tearing off with a pair of fine pointed forceps the portion of the 

 epiderm from which they spring, care being taken not to grasp the 

 hair itself, whereby such an injury would be done to it as to check 

 the movement within it. The apochromatic hair should then be 

 1 Quart. Journ. of Microsc. Science, vol. iii. (1855^, p. 277. 



