OCR Text |
Show ()8 CIRCUMNUTATION OF SEEDLINGS. CHAP. II. types amongst plants, were. co~tinually circumm~tating, we may infer that th1~ k1nd of movement 1s common to every seedling spemes. Sun-KINGDOM I.-Phmnogamous Plants. Class I.-DrooTYJ,EDONS. Sub-class !-Angiosperms. Family. 14. Crucifcrce. 26, Caryophyllece. 36. J11alvacece. 41. Oxalidece. 49. TropaJ,Jlece. 52 . .A urcmtiacace. 70. Hippocastanl'ce. 7 5. Leguminosce. 1 Oil. Cucw·bitacece. l 09. Cactew. 122. Compositce. 135. Primulacece. U-5. Asclepiadece. 151. Convolvulacece. 1S4. Borraginece. 15o. Nolanece. 15 7. Solanece. 181. ClienopocUece. 202. Euph01·biacece. 211. Cupuliferce, 212, Corylacew. Cohort. II. PARII::TALES. IV. CAnYOPm'LLALES. YL l\1ALVALES. V 1!. GERANIALI::S. Drrro DITTO X. SAPINDALI!:S. XI. ROSALES. .X II. P ASSIFLORALES. XIV. FICOIDALES. XVII. AS'rRALES, XX. PRIMULALES. XXII. GENTIANALES. XXIII. POLEMONIALES. DITTO DITTO XXIV. SOLANALES. XXVII. CuENOPODIALtcs. XXXII. EUPUORI31A!,ES. XXX VI. QUERNALES. DITTO Sub-dues II - Gyrnnospe1·ms. 22:·t Conife, ·(JJ. 2:24, Cycadece. Class II.·-MoNoooTYLEDONS. 2. Cannacece. 34. Liliace(JJ, 41. Asparagea:. 55. Graminece.' II. AMOl1ALES. XI. LILIALES. DITTO XV. GLUMALES. SuB-KINGDO~ II.-Crypt.,gamio Plants. 1. Filices, I. FILICALES. 6, Lycopodiacea:. DITTO CHAP. II. ACTION OF THE RADICLE. Radicles.-In all the germinating seeds observed by us, the :first change is the protrusion of the radicle, which immediately bends downwards and endeavours to penetrate the ground. In order to effect this, it is almost necessary that the seed should be pressed down so as to offer some resistance, unless indeed the soil is extremely loose ; for otherwise the seed is lifted up, instead of the radicle penetrating the surface. But seeds often get covered by earth thrown up by burrowing quadrupeds or scratching birds, by the castings of earth-worms, by heaps of excrement, the decaying branches of trees, &c., and will thus be pressed down; and they must often fall into cracks when the ground is dry, or into holes. Even with seeds lying on the bare surface, the :first developed root-hairs, by becoming attached to stones or other objects on the surface, are able to hold down the upper part of the radicle, whilst the tip penetrates the ground. Sachs has shown* how well and closely root-hairs adapt themsel~es by growth to the most irregular particles in the soil, and become :firmly attached to them. This attachment seems to be effected by the softening or liquefaction of the outer surface of the wall of the hair and its subsequent consolidation, as will be on some future occasion more fully described. This intimate union plays an important part, according to Sachs, in the absorption of water and of the inorganic matter dissolved in it. The mechanical aid afforded by the root-hairs in penetrating the ground is probably only a secondary service. The tip of the radicle, as soon as it protrudes from the seed-coats, begins to circumnutate, and the whole * 'Physiologie V egctn.le,' 1868, pp. 1!'19, 205. |