132 



CIRCULATION IN CELLS. 



Circulation in vegetable cells. 



Circulation in Tradescantia. 



Fi 9- 52 - circulation in vegetable cells is shown by the di- 



rection of the arrows in Fig. 52. The course taken 

 by the current may be determined under the mi- 

 croscope by the minute floating, or, rather, drifting 

 granules. It is to and then from the nucleus. 



fig. 53 represents one of Fig. 53. 



the jointed hairs from the 

 Tradescantia Yirginica. The 

 engraving is from the view 

 given by Mr. Slack, correct- 

 ed, however, by the aid of a 

 photograph of a similar ob- 

 ject, a, ^ c, d are the suc- 

 cessive cells of the hair. The 

 dotted lines show the direction of the current to 

 and from the nucleus. 



The juice which is about to nourish a part has 

 Circulation ^ or *^at P art a certam affinity, but, with the accomplishment 

 through per- of that nutrition, the affinity is at once lost. Thus, for in- 

 us parts. gtance? i n the systemic circulation, the parts to be nourished 

 have a certain affinity for the arterial blood ; they take from it whatever 

 their purposes require, and, that done, the relation at once ceases ; the 

 blood, become venous, has lost its hold upon them, and is pressed off. 

 We may conveniently describe this effect as a pressure of the unchanged 

 upon the changed liquid. 



The motions of the sap in plants are clearly dependent on this prin- 

 Expianation of ciple. Leaving out of consideration the minor movements 

 scenTof tbfslp w ^ cn ta ^e place for special purposes, or at specific epochs 

 of plants. in the development, it may be truly said that the nutritive 

 changes occurring in the leaf are the primary cause of the motion ; for, as 

 the ascending sap presents itself on the sky face of the leaf, it receives 

 carbon, under the influence of the sunlight, from the air, and becomes con- 

 verted into a gummy, glutinous liquid. And just as in the pores of a 

 bladder, or in those of any pervious mineral, pure water will drive out 

 gum-water, and occupy the pore, so will the ascending sap expel the 

 gummy solution from the capillary tubes or intercellular spaces of the 

 leaf. As fast as this takes place, the active liquid becomes inactive, by 

 itself changing into a gummy solution, and the movement is perpetuated. 

 And this ensues not only in the leaf, but in every part of the plant ; the 

 liquid to be changed presses upon that which has changed, and forces 

 it onward. In this manner, motions in various parts and of very great 

 intricacy will ensue, but all of them, if duly considered, no matter 

 whether their seat be in the root or in the bark, in the flowers or in the 



