366 



STRUCTURE OF PHANEROGAMIC PLANTS. 



FIG. 153. 



13 



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 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 its circulation. The hair should then be 

 placed with a drop of water under thin glass ; and it will gene- 

 rally be found advantageous to use a l-8th in. objective, with an 

 achromatic condenser having a series of diaphragms. The nature 



of the movement in the hairs of 

 different species of plants is far 

 from being uniform. In some in- 

 stances, the currents pass in sin- 

 gle lines along the entire length 

 of the cells, as in the hairs from 

 the filaments of the Tradescantia 

 virginica or Virginian spider-wort 

 (Fig. 153, A) ; in others, there are 

 several such currents which retain 

 their distinctness, as in the jointed 

 hairs of the calyx of the same 

 plant (B); in others, again, the 

 streams coalesce into a network, 

 the reticulations of which change 

 their position at short intervals, 

 as in the hairs of Grlaucium luteum; 

 whilst, lastly, the current may flow 

 in a sluggish uniformly moving 

 sheet or layer. Where several dis- 

 tinct currents exist in one cell, 

 they are all found to have one com- 

 mon point of departure and return, 

 namely the "nucleus" (B, a); from 

 which it seems fairly to be inferred, 

 that this body is the centre of the 

 vital activity of the cell. 1 Mr. 

 Wenham states that in all cases in 



Circulation of fluid in hairs of Tradescantia which the Sap-motion is Seen ill 



Virginica: A, portion of cuticle with hair the hairS Ot a plailt, the Cells OI 



attached; a, b, c, successive cells of the hair; the CUticle also display it, prO- 



d, cells of the cuticle; c, stoma: B, joint of a T j ,-t , ,1 11 



vided that their walls are not so 

 opaque or so strongly marked, 

 as to prevent the rotation from 

 being distinguished. 2 The cuticle may be most readily torn off 



1 The above statement is called in question by Mr. Wenham, who affirms that " when- 

 ever he has observed such a 'nucleus,' it has either been formed by an -accidental con- 

 glomeration of some of the cell-contents, or by morbid conditions." The Author is satisfied, 

 however, from the constancy with which the " nucleus" is the centre of the diverging 

 lines of protoplasm, in those cells which have several streams radiating from one point, 

 that it can neither be an accidental nor a morbid conglomeration. 



2 Op. cit. vol. iv. p. 44. 



nucleus. 



