13 



mfttityn both in plants and animals is well seen in the lower organisms, 

 which, a green-^that is, il containing chlorophyll — move towards the 

 light J but a ifchey have no chlorophyll, light has no special influence 

 in determining their movements. Hence the motion witnessed would 

 seem to be. depended on the decomposition of carbonic acid gas, and 

 the elimination of oxjrgen, which talses jdace under such circum- 

 stances as already explained. The (protoplasm which lines the cells 

 has contraetile powers, and these contractile powers are, as we have 

 seen, set in action by the stimuli of light or heat, and probably by 

 electridty. 



"Thjere ape other njiovemeiits in plants evincing sensibilily. Human 

 beingsj^re apt_ to blush on the occasion of suddep strong emotions, 

 and this bljjshing is ijjie ,to a sudden turgeseence of the iliinute vessels, 

 induced by their momen,tary dila,t3.tion. Plaflts execute ^movements, 

 due, lj|ce blushing, to varying amount^ of turgeseence. In most active 

 vege,t,9.bje cells currents of jjuids may be p|bserved. These currerits 

 are pot entirely dependent on contraction of ,the protoplasm, but on 

 the varying degrees of albspption .ma,nifested in it. If one portion 

 Buddenjly exerts a great pq^er of a])sprbing water, tliere is a corre- 

 spouding flow to pieet the d,emaud, hepce i,inb;ibitjon ca,nses turgeseence, 

 and the turgeseence gives rise to the formation of currents in individufl 

 cejl^. When ^ ni^mEe? of such c^lls are plosely packed together, and 

 are influenced in the same w^y, not only is ;liher,e 3, flo:w in the^ells 

 in<|i,y3;dij,a3ly, but tliere ^ a riisb of iBuid from cell to cell, ^nd conse- 

 q^ui^ntly a movein^ent throughout the ;whole organ thus affected. In 

 this ;^a,y th^e ojpe^ng jand closing of flowers, ,as ;vrell as the f oldiing apd 

 upfoldiiig pi leaves, may t,o ^ome extent be accoi^nt,ed for. The c,ij;rjiQus 

 mpyemient of jfche sensitive plants are tp be explained in a simila,r 

 manner by tlie swellipg ;0f certain of theiir tissue^s, this |;urg;escence 

 being stimulated or set in action !by certjain stimuli, and checkeij by 

 otl^ieys. pj^mljing plants ajnd some |tendry^ exhibit t^VP different kinds 

 of jppvements— the oj;ie a gp9ntaneou,s revolving power manifested in 

 yoixftg aptiye 8jj,oois, in some plants in one direction, ip other? in jthe 

 coiil^airj. The ol;)ject of jtbese ;revolptions i? to allow the stem to 

 attach rts^f to sopie gijipport round which it may twine. How they 

 are affected is npt .understppd ; they seern to be spont^iieou?, and 

 not under the influence of e;s:temal copdi'tiops. The movements of 

 nipst tendnls, however, are directly excited iiy contact. A slight 

 touch cai^ses thenj to move. Ip orchids (see tjie labejlum of Pterostylis, 

 Cfafeifna, 4i,c-), and in piapy flowering pj.ants, displacements take^placp 

 in the stamep^ (s,ee jBerher^ii), xti thje styje (see coj-umn in Sfi/Udium), or 

 in jjip poiil,ep itseli, these uipve.piepts being apparently dependent on 

 coptractjpp pj£ the prptoplasm, or on varying hygrometric conditions, 

 llepee, ,tpen, ,sp f a^ ji,s realipg goes, if we a.d,mit aensi|iyeness ,^s the 

 eq,uiyaleiat of sepsa^apn, w;e ca(npot d.eny tjhat a plant possesses tlie 

 same fpjculty as an apipial. If we tajke lo'coniotion or the power of 

 translation irom place tp plac^, opce copsjidpred distipctiye of ^.nimal?, 

 Wfi .shall ;fipd it is possessed by vegetable^ as well. This is ppen ip 

 cer;iia,in organs of j.'ep;rpductiop cp,lled zoospores, and in t^e 

 antjieronoids of Alg© and other cryptoganious plants. The movement 

 in flill likelthpod depends on the /agitatiop of the flpe ^ilias or thfeiads 

 wil^ \W|Kip^ these organisms are furjijishejd,; |but we ,are .^tall 

 ignorant as io tlie cause that excites the vibration of .the ail(ia. 



