358 



THE MICROSCOPE AND ITS REVELATIONS. 



FIG. 240. 



this amplification, the phenomenon may be best studied in the single 

 layer of marginal cells; although, when a lower power is used, it is most 

 evident 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 usu- 

 ally from l-3000th to l-5000th of an inch in diameter. When the rota- 

 tion is active, the greater number of these granules travel round the mar- 

 gin of the cells, a few, however, remaining fixed in the centre: their rate 

 of movement, though only l-40th of an inch per minute, being sufficient 

 to carry them several times round the cell within that period. As in the 



case of the 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. Wen ham at no 

 more than 1-20, 000th of an inch. 

 When high powers and careful illumi- 

 nation are employed, delicate ripples 

 may be seen in the protoplasmic cur- 

 rents. 1 



355. 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 observ- 

 able in the hairs of the Epidermic sur- 

 face; and according to Mr. Wenham, 2 

 who has given much attention to this 

 subject, " the difficulty is to find the 

 exceptions, for hairs taken alike from 

 the loftiest Elm of the forest to the 

 humblest weed that we trample beneath 

 our feet, plainly exhibit this circula- 

 tion." 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 



Rotation of fluid in Hairs of Tradescantia , 111 n , i j i i jx -,-1 



Virginica: -A, portion of cuticle with hair should be detached by tearmg-off with 



attached; a, b, c, successive cells of the hair; p -naii. n f finp nninfprl frrppr><? thp r>nr- 



d, cells of the cuticles; e, Stoma:-B, joints a . P a11 QQpS, . 



of a beaded hair, showing several currents: tion of the Cuticle 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 hair should then be placed with u 

 drop of water under thin glass; and it will generally be found advantage- 



1 ' Quart. Journ. of Microsc. Science," Vol. iii. (1855), p. 277. 



2 ' On the Sap-Circulation in Plants,' in " Quart. Journ. of Microsc. Science, ' r 

 Vol. iv. (1856), p. 44. It is unfortunate that Mr. 'Wenham should have used the 

 term * circulation ' to designate this phenomenon, which has nothing in common 

 with that movement of nutritive fluid through tubes or channels, to which the 

 term is properly applicable. 



