DEPRESSED GROWING-POINTS. 



463 



necessary protection by the depression of a growing-point in a mass of resistent tissue, 

 which at the same time abounds in nutritive substances ; since such arrangements as 

 that in the figure occur chiefly in tuberous and bulbous plants, the entire vegetative body 

 of which perishes annually, leaving behind in the soil only these organs from which 

 new individuals subsequently arise. 



Depressed growing-points are everywhere common in the development of young 

 flowers, or even young inflorescences, where 

 it is also usually important that a protective 

 hollow structure should be formed, in which 

 the very tender young parts of the flower, 

 and especially the ovules with their con- 

 tained embryos, are then to be produced. 

 A somewhat more complicated case of this 

 kind is presented in Fig. 300, which repre- 

 sents the longitudinal section of a young 

 flower bud of Geum rivale, a plant belong- 

 ing to the Rosacese. The growing-point, 

 X, here projects in the form of a cone from 

 the bottom of a cup-like hollow structure 

 yy, the inner side of which, at least at the 

 basal portions, likewise consists of embry- 

 onic tissue, from which the young stamens a are arising. The elongation which 

 subsequently sets in, in this case results in that the wall yy of the hollow structure 

 beconies extended like a flat plate ; fh the Rose, however, and in many other cases, 

 the part yy also subsequently forms a hollow cavity, open above by means of a 

 narrow mouth only. The depressed growing-point, x, of the flower, produces at its 

 outer margin numerous small leaves, which subsequently grow together at their edges 

 and constitute the so-called ovaries, in each of which an ovule arises. 



FIG. 299. — Development of tubers of Gagna pratensis (after 

 shoot-axis ; b leaf-sheath, in the axil of which the 

 bud k with the tuber t has been produced. 



Irmisch). 



subject. For this purpose I may mention those from which I have myself derived the best instruc- 

 tion in years gone by — above all the fundamental works of Naegeli, as follows : — 



' Zeitschrift fiir wiss. Bot., ' Schleiden und Naegeli (Zurich, 1 844-46), the memoirs on CauUrfa, 

 Delesseria, laws of growth of Mosses and Liverworts, Polysiphonia, and several other treatises. 



' PJlanzenphysiol. Untersuchungen,' Naegeli und Cramer, Heft I, 1855, growth oi Pterotham- 

 nium, Hypoglossum, the leaf of Sphagnum, leaf of Aralia ; also Heft IH, on Lycofodium and 

 Equisetum (by Cramer). 



Further, ' Beitrage zur wiss- Bot.' Naegeli, Heft I (Leipzig, 1858), ' ffber das Wachsthum 

 des Stammes und der Wurzeln von Gefdsspflanzen,' and H. 4, ' Enstehung und Wachsthum der 

 Wurzeln' by Naegeli and Leitgeb (Miihchen, 1867). On roots also, ■ Mecherches sur I'accroissement 

 terminal des racines,' by E. de Janczewski, in Ann. des sc. nat., Ser. 5 (Paris, 1874). 



Also ' ffber den Vegetationspunkt der Angiospermenwurzeln,' H. G. HoUe, Bot. Zeit., 1876, 

 No, 16. 



'Zur Entwicklungsgeschichte des Blattes.' Dissertation by A. W. Eichler (Marburg, 1861). 



' S>ie Scheitelzellgruppe im Vegetationspunkt der Phanerogamen,' J. Hanstein, in Festschrift der 

 niederrhein. Ges.fUr Natur- und Heilkunde. 



' Traiti d'organoginie comparie de lajleur' by J. B. Payer (Paris, 1857). 



' Recherches sur la ramification des Phanirogames' by M. Eug. Warming (Copenhagen, 1873). 



'Die Coniferen und die Gnetaceen' Strasburger (Jena, 1872). 



That many other treatises may be named in addition to these comprehensive works has already 

 been stated. 



