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Show 520 l\WDIFIRD CIRCUMNUTA'l'ION. UHAl'. X. minal blcach~cl. portion w.us a little ~~~rivcll cd. AR the gy110 _ phor~s ar~ rigid ancl ansc ~rom .st~ft braJJchc::;, all(l as they termmatc m sbn,I'P smooth pomts, It Is pl'Obttl>le tll::tt they could penetrate the ground l>y the mere force of growth. Bnt thi. action must be aided by tho ci1·cumnutati11g movement, for fine sand, ko1~t moi~t, was prossed close ronnel il10 avcx of a gynophore wh1ch hn,d renchod tho ground, and after a row hours it was sunounded by n nnnow open crack. After three weeks this gynophore was uncovoror1, and the n.pex was fonud at a depth of rather allove half an inch dcvelOJ)ell .ill to tt :•mall, white, ovalJJocl. Amphicarpceu monliiCit.-Thil-3 plant produces long thin shoots, "\vhid1 twine round a support n,nd of coun;e circmnnutate. Early in tho summer shorter shootH nrc procluccd from the lower parts of tho plant, which grow perpendicularly downwards and penetrate tho ground. One of those, tormi11ating in a minute bud, was observed to bury itself in sand to a depth of 0-2 inch in 24 h. It wn,s lifted up and fixed in an inclined position about 25° beneath tho horizon, being feebly illuminated from above. In this position jt doHc1·ibcd two vertical ellipses in 24 h.; but on tho following da.y, when Lro1 1ght into tho bonso, jt circumnutn,ted only a very little round tho same spot. Otlwr branches were seen to poucLrato the ground, nlHl were aft rwn, rds found running bko roots bmJCath tho ~;m!'aco for a length of nen,rly two inches, and they had grown thick. Ono of these, after thus rnnnino·, had emerged juto the air. Uow fnr circumnuta- tion aids these delicate bmnchos in entering tho ground we do not know; but tho rofloxod hn,irs with whicl! they me clotheu will assist in the work. This plant produces )Jodr' in tlto air, and others beneath tbo grouml; which dill' l' greatly in appearance. Asa Gray says* that it is tl1o impcrfi·ct flowers on the creeping branches ncnr the base of tho pln,nL which prorluce tbo subterranean pods; those flowers, therefore, must lmry themselves like those of Arachis. But it may be r-;uspcctod that the branches which were seen by us to po11otrai.o tho ground also produce subterranean flowers and pods. DrAGEO'l'HOPISl\L Besides geotropism and npogeotropism, t]wro is, according to Frank, an allied form of moYcment, - * 'Manual of the Botany of the Northcm Uniteu Statce,' 185G,p. 106. GliAl'. x. DIAGBOTHOL'L 'i\I. 521 ly "trausverse-o-eotrOI)ism," or diageotropism, as mtlllO , ' b , " • we may call it for the sake of nu1.tc~m~ our oth:r terms. Under the influence of grttntatwn corta111 parts are excited tc_) plac~ thmr:sol :os more or los.· transversely to the hno of 1ts actwn. We made no observations on this subject, anrl will here o_nly re-. mttrk that the position of the secondary ntchclos of mrious phmts, which extend hori)t.ontt1.lly or are a little inclined downwards, woulcl proLaLly be consirlered l>y Fn"tnk as clue to transverse-geotropism. As it has been shown in Chap. I. that the seeonclary rauicles of Oucurbita mn<lo serpentine tracks on a smoked glass-plate, they clearly circunnmtate<1, and there can hardly Le a douLt that this holus good with other secolHlm·y ra<1iclos. It seems ther~fore highly proLable that they place themselves 1n their diagootropic position by means of mouifie(l circumuutation. Finally, we may conclu<le tht"tt the three kinds of movement which have now Goon clcscribccl and whi ·h t\l'e excited by gravitation, consist of modified circumnutation. Different parts or organs on the same plant, ILUU the same part in clifforont species, are thus xcitr(l to act in a widely different manner. vVe Cttn see nu reason why the attraction of gmvity should directly modify the state of turgescence and subsequent growth of one part on the upper side and of another part on the lower side. We ate therefore led to infer that both geotropic, apogcotropic, and diageotropic movements, the purpose of which we can generally understawl, 1, • El~ving has lately describotl ;~rbetteu des Bot. Instituts in Wurzburg,' li. ii. 1880, p. 489) au excdlent instam·o of sueh movemoliiS in tho 1hizomos of certain plo.utt>. |
