Fig. 54.  Selaginella Kraussii (?):  circumnutation of young plant, kept in darkness, traced from 8.45 A.M. to 10 P.M.  Oct. 31st. [page 67]

CHAPTER II.

GENERAL CONSIDERATIONS ON THE MOVEMENTS AND GROWTH OF SEEDLING PLANTS.

Generality of the circumnutating movement—­Radicles, their circumnutation of service—­Manner in which they penetrate the ground—­Manner in which hypocotyls and other organs break through the ground by being arched—­ Singular manner of germination in Megarrhiza, etc.—­Abortion of cotyledons--Circumnutation of hypocotyls and epicotyls whilst still buried and arched--Their power of straightening themselves—­Bursting of the seed-coats—­ Inherited effect of the arching process in hypogean hypocotyls—­ Circumnutation of hypocotyls and epicotyls when erect—­Circumnutation of cotyledons—­Pulvini or joints of cotyledons, duration of their activity, rudimentary in Oxalis corniculata, their development—­Sensitiveness of cotyledons to light and consequent disturbance of their periodic movements--Sensitiveness of cotyledons to contact.

The circumnutating movements of the several parts or organs of a considerable number of seedling plants have been described in the last chapter.  A list is here appended of the Families, Cohorts, Sub-classes, etc., to which they belong, arranged and numbered according to the classification adopted by Hooker.* Any one who will consider this list will see that the young plants selected for observation, fairly represent the whole vegetable series excepting the lowest cryptogams, and the movements of some of the latter when mature will hereafter be described.  As all the seedlings which were observed, including Conifers, Cycads and Ferns, which belong to the most ancient

* As given in the ‘General System of Botany,’ by Le Maout and Decaisne, 1873. [page 68]

types amongst plants, were continually circumnutating, we may infer that this kind of movement is common to every seedling species.

Sub-kingdom I.—­Phaenogamous Plants.

Class I.—­Dicotyledons.

Sub-class I.—­Angiosperms.  Family.  Cohort. 14.  Cruciferae.  II.  PARIETALES. 26.  Caryophylleae.  IV.  CARYOPHYLLALES. 36.  Malvaceae.  VI Malvales. 41.  Oxalideae.  VII.  GERANIALES. 49.  Tropaeoleae.  Ditto 52.  Aurantiaceae.  Ditto 70.  Hippocastaneae.  X. SAPINDALES. 75.  Leguminosae.  XI.  Rosales. 106.  Cucurbitaceae.  XII.  PASSIFLORALES. 109.  Cacteae.  XIV.  FICOIDALES. 122.  Compositae.  XVII.  ASTRALES. 135.  Primulaceae.  XX.  PRIMULALES. 145.  Asclepiadeae.  XXII.  GENTIANALES. 151.  Convolvulaceae.  XXIII.  POLEMONIALES. 154.  Boragineae.  Ditto 156.  Nolaneae.  Ditto 157.  Solaneae.  XXIV.  SOLANALES. 181.  Chenopodieae.  XXVII.  Chenopodiales. 202.  Euphorbiaceae.  XXXII.  EUPHORBIALES. 211.  Cupuliferae.  XXXVI.  QUERNALES. 212.  Corylaceae.  Ditto