H6 



MORPHOLOGY OF TISSUES. 



skin of the hand which touches the leaf. (For further details on the Morphology of 

 Hairs cf. sect. 22.) 



Fig. 72. — Development of the hairs on the calyx of a flower-bud oi Althu-a rosea (X300) ; A wh woolly-hairs of the inner 

 side ; b and c glandular hairs in different stages of development ; at a (to the right) rudiment of a glandular hair ; 

 ep always signifies the (still young) epidermis. The figures a.'\n A,^ (to the left) and "y (to the right below) show the first 

 stages of development of the stellate hairs (or rather tufts of hairs), the subsequent condition of which may be compared 

 in Fig. 44 (p. 43) ; at ^ a is the hair in longitudinal section ; /3 and y show the appearance seen from above ; the cells 

 are rich in protoplasm ; the formation of vacuoli (->) in the protoplasm is beginning in y. 



T:he Stomata^ are always absent from the epidermis of true roots; on the other 

 hand they are usually present on underground axial organs and leaves ; even on sub- 

 merged parts they are occasionally found (Borodin, /. c.) ; but they are formed in the 

 largest numbers on the aerial internodes and leaves, but are not altogether absent 

 from the petals and carpels ; they are even formed in the interior of the cavity of the 

 ovary (e.g. in Ricinus). They are most abundant where an active interchange of gases 

 takes place between the plant and the surrounding air ; for, considered physiologi- 

 cally, they are nothing more than the mouths of the intercellular spaces of the inner 

 tissue which open in places externally between the epidermis-cells ; this is however 

 always preceded by a peculiar development in a young epidermis-cell. Since the stomata 

 do not arise till rather late, that is during or after the expansion of the internodes and 

 leaves, their arrangement is partially dependent on the already elongated form of the 

 epidermis-cells ; if these are greatly elongated in one direction and arranged in rows 

 (as in Equisetum and the stem and leaves of many Monocotyledons, and Pinus), the 

 stomata also appear arranged in longitudinal rows (the cleft lying in the direction of 

 the axis of groAvth, the guard-cells right and left) ; if the epidermis-cells are irregular 

 on a superficial view, curved, &c., the position of the stomata is more undefined and 



^ H. von Mohl, Verm. Schriften bot. Inhalts, pp. 245, 252. Tubingen 1845. — Ditto, Bot. Zeitg. 

 p. 701, 1856. — A. Weiss, Jahrb. fiir wiss. Bot. IV, p. 125, 1865. — Czech, Bot. Zeitg. p. loi, 1S65. — 

 Strasburger, Jahrb. fiir wiss. Bot. V, p. 297, 1866.— E. Pfitzer, ditto, VII, p. 532, 1870. — J. Rauter, 

 Mittheil. der naturwiss. Vereins fiir Steiermark, vol. II, Heft 2, 1870. — Borodin, Bot. Zeitg. p. 841, 

 1870. — Hildebrand, ditto, p. 1. — Ditto, Einige Beobachtungen aus dem Gebiete der Pflanzen- 

 anatomie. Bonn 1861. 



