366 



STRUCTURE OF PHANEROGAMIC PLANTS. 



Fio, 



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 

 diiferent 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 Tradegcantia 

 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 Glaucium luteum; 

 whilst, lastl}', 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.' Mr. 

 Wenham states that in all cases in 

 which the sap-motion is seen in 

 the hairs of a plant, the cells of 

 the cuticle also display it, pro- 

 vided that their walls are not so 

 opaque or so strongly marked, 

 as to prevent the rotation from 

 The cuticle may be most readily torn off 



CircQlBtion of fluid ill hairs of Tradescantia 

 Virginica: — A, portion of cuticle with liair 

 attaciied ; a, 6, c, successive cells of the hair; 

 d, cells of the cuticle; e, stoma: — b, joint of a 

 beaded hair, showing several currents ; a, 

 nucleus. 



being distinguished.' 



'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. 



^ Op. cit. vol. iv. p. 44. 



