REJUVENESCENCE IN NATURE. 107 



stetter on the structure of the grass-plant.* All these 

 attempts to compose the plant of leaves are wrecked upon 

 the fact of the existence of the stem as an original, inde- 

 pendent and connected structure, the more or less distinct 

 articulation of which certainly depends upon the leaf- 

 formation, but the first formation of which precedes that 

 of the leaves. The graduated metamorphosis of the plant 

 requires the stem as a bridge between the steps ; the 

 theory of the arrangement of leaves requires it as the basis 

 upon which the leaves form their regulated ranks ; the 

 comparative morphology of the lower plants demonstrates 

 the independence of the stem, since it never shows leaves 

 without stem, although certainly stem-formation without 

 leaves ;f finally the history of development brings the 

 stem before our eyes, in its earliest period of formation, 

 as the visible foundation, out of which the leaves are 

 developed, j 



* ' Jahreshefte des Vereins fur Vaterlandische Naturkunde in Wurtem- 

 burg,' 1847, p. 1 ; and 1848, p. 144. The leaf and the segment of the halm 

 beneath it form, according to Hochstetter, a whole, which he calls a stage or 

 storey (Stockwerk), and which consists of three parts, the foot (internode of 

 the halm), the trunk (the leaf-sheath), and the head (the blade of the leaf). 

 Each new stage is produced from its predecessor by a branch being given 

 off at the node between the foot and the trunk. In this way each leaf is 

 regarded as the terminal prolongation of the mternode of the stem, which 

 original relation is supposed to be clearly preserved in Juncus, on the round 

 stalk-like and erect highest leaf (according to Hochstetter, homologous with 

 the point of the sterile halm), from which we see the inflorescence escape 

 laterally through a slit. Hanstein also regards the leaf as terminal, since he 

 asserts that each new leaf originates through uplifting of the centre of the 

 point of vegetation : "Puncti vegetationis centrum in novum extenditur 

 folium," 1. c., p. 83. 



f In the higher classes of plants even we meet with cases of the develop- 

 ment of the stem without leaves, as well-known in tendrils and thorn- 

 structures. The sterile halm of the Rushes (Juncus conglomerates, &c.) 

 affords an equally familiar, though less noticed case. 



J The recent researches on the commencement of leaf-formation leave no 

 doubt on this point. See the works of Schleiden, especially on the origin of 

 the cotyledons in the embryo and the coats on the nucleus (' Wiegmann's 

 Archiv, 3 1837, and elsewhere); VonMercklin (' Zur Entwicklungsgeschichte 

 der Blatt-gestalten,' 1846 : on the development of the forms of Leaves, 

 trans, in ' Ann. des Sc. nat., 2d ser. Botanique,' torn, vi, p. 215, 1846) ; Adr. 

 de Jussieu, on the formation of the embryo of Monocotyledons (' Ann. des Sc. 

 nat.' Juin, 1839) ; Duchartre, on the organogeny of the parts of the flower 

 of the Ouagracea;, Primulaceffi, Malvaceae, Nyctagineae ('Ann. des Sc. nat./ 

 184-2-4-5-8.) Even in the Ferns, in which the leaf-nature of the frond, as 



