234 



MONTHLY JOURNAL OF AGRICULTURE. 



fluid, and the result is a gradual thicken- 

 ing of the membrane composing the \\'all of 

 the cell, and likewise an eventual separation 

 of the mass itself, either laterally or longitu- 

 dinally, into two, each becoming a sepai'ate 

 center of motion. The currents thus dis- 

 turbed, the inner coat of the cell begins to 

 contract between tliem, as exhibited in the 

 left-hand figin-e, dividing it into two cavities, 

 which are afterward more or less extended 

 by the force of tlieir respective cun-ents. 



Although no apparent connection exists 

 between the cavities of the contiguous cells, 

 careful and repeated observation shows that 

 the movements of the fluids in each influ- 

 ence those of their neighbors, and that a re- 

 ciprocal action is maintained throughout the 

 whole livuig fabi'ic. The uniformity of direc- 

 tion preserved by the currents in different 

 cells is in accordance with this latter circum- 

 stance, and is beautifully exemplified in the 

 etems and v^'horled branchlets of the " cha- 

 racea?," another tribe of aquatic plants, a 

 grade or two higher in the scale of vegetable 

 organization than the •' confervse." 



Fig. 2. 



Figure 2 represents a portion of "nitella 

 flexilis," gi'eatly magnified, the arrows mark- 

 ing the course of the internal currents (more 

 distinctly shown in the farther magnified 

 view on the right) of the two terminating 

 cells of one of the branchlets ; from inspec- 

 tion of which it will be understood how a 

 complete rotation of the fluid takes place in 

 each cell, passing upward on one side and 

 returning on the other, and that a similarity 

 of movement obtains throughout each whorl 

 of branclilets ; the ascending current being 

 toward the outside of the plant, the descend- 

 ing toward the inner or axial side of the 

 whorl. These motions are more or less rapid, 

 according to the season or the temperature 

 ■under which the examination is made. In 

 the winter time they are scarcely observable. 



In what degree the flow of the sap in the 

 higher orders may resemble these curious 

 phenomena, we have not at present the means 

 (474) 



of ascertaining. The different condition of 

 the woody tulies which contain and conduct 

 it, as compared with that of the cells we have 

 examined, may involve considerable diversity 

 of organic action ; and it would be absm-d to 

 endeavor to deduce any general conclusions 

 from so very partial an acquaintance with a 

 few isolated facts ; the more importvuit and 

 ultimate phenomena of vegetable physiology 

 are yet as much a mystery to human specula- 

 tion as is the source of life itself. 



The relative distribution of the minute ele- 

 mentary organs described in our last Lecture 

 varies in different plants, and, as we shall see 

 hereafter, occasions organic distinctions of 

 high importance to the practical as well as to 

 the merely theoretical student. But under 

 whatever an-angement of the vital channels 

 and recesses the existence and development 

 of the vegetable are maintained, the general 

 process is probably not very dissimilar be- 

 tween the highest and the lowest ; the most 

 complicated and the simplest of their struc- 

 tures being rather modified than changed for 

 the i-equired adaptation. Tiie difference be- 

 tween the foodful and the poisonous, 

 in all their degrees of quantity and 

 intensity, are produced by causes 

 which are only secondary or subsidi- 

 ary to those that regulate the action 

 of the main-springs of vegetable life. 

 In all the higher orders of plants the 

 absorption of nutriment by the root 

 is but a small, however necessary, 

 portion of a complicated process, in- 

 volving a vast amount of vital and 

 chemical action, whose conjoined ef 

 fects are witnessed in the production 

 of those secretions that give them 

 character or property and value in the 

 domestic economy of Man. The first 

 elaboration of the absorbed nutriment 

 changes it into sap — a fluid possessing 

 nearly the same general characters in 

 all plants, though unquestionably the 

 medium from which their most diver- 

 sified products are secreted by subse 

 quent modification of its original com 

 ponent principles and (as it woukl apjiear 

 in some instances at least) the addition of 

 others. Leaving, however, these latter, and 

 the sources of their derivation, to be dis- 

 cussed at a future period, we will now ex- 

 amine the structure through which the sap is 

 conveyed, and the adaptation of the external 

 organs traversed by its channels to the fulfill- 

 ment of the changes which it is destined to 

 undergo. 



The popular notion respecting the func- 

 tions of the root are very incoiTcct, it being 

 generally regarded as the sole medium 

 througli which nourishment is conveyed to 

 the plant ; while, so far from such being the 

 case, almost every other part presents mors 

 or less of an absorbing surface :- not, perhaps, 

 in constant or unifonu action, but capable ol 

 so adapting itself under pecnliar circum- 

 stances. Some plants, especially those of 

 slow growth and succulent habit, will live 



