90 



CELLULAR TISSUE. 



and treated with dissolving reagents— e. g. alcohol or ether— is intercalated between 

 cell-membrane and cuticle. 



The same phenomenon, in the main, occurs in the multicellular heads of the 

 bladder-like glandular hairs, villi, and scales. The thickening by the secretion 

 begins in these cases at a point more or less near the apex of the whole (not on 

 each or on several single cells) and extends from this point centrifugally, varying 

 greatly in extent and bulk according to the special cases. The outer walls of 

 the single cells thus form with one another either a smooth, even, or domed 

 surface, or they arch outwards hke papillse into the secretory mass which overlies 

 them, and is in its turn bounded by the cuticle. The raised cuticle itself is usually 

 homogeneous and structureless, in other cases (shield-like scales of Humulus, 

 Ribes nigrum) it is marked off into areas corresponding to the lateral limits of the 

 cells. As already intimated the glandular structure in hairs is not always restricted 

 to the head ; it may also occur on the lateral wall of capitate hairs, and of such as 

 are not capitate as in Cistus. (Fig. 36.) 



From the point of insertion of glandular hairs in the buds of Rumex, Rheum, 

 Cunonia, Coffea, Alnus, CarpinuB, Corylus, &c., the glandular structure of the walls 



extends over the smooth epidermis (Hans- 

 tein, Bot. Ztg. 1868). This attains thereby 

 the properties of the glandular surface. 

 The same occurs in exquisite form on 

 the sticky young shoots of Betula alba 

 (Fig. 35), where the glandular nature of 

 the wall of the shield-like glandular scales 

 extends over the whole epidermis, as far 

 as the ridge of entry of the stomata, 

 where it ceases. The sticky zones under 

 the nodes of Lychnis viscaria and other 

 Silenese appear to be of the same nature, but require more careful investigation. 



Limited, bladder-like glandular surfaces, that is glandular spots, in the above- 

 defined sense (neglecting the nectaries of flowers, which will not be here treated of), 

 occur in solitary cases on smooth surfaces, as on the under side of the leaf of Prunus 

 lauro-cerasus, Clerodendron fragrans, or on the ends of emergences without vascular 

 bundles, as the capitate ends of the villus-hke prickles of Rosa *, the glandular warts 

 of the branches of Robinia viscosa ^ ; but the principal place of their occurrence is 

 on leaves and leafy parts over peripheral endings 0/ vascular bundles, sometimes on 

 the surface, sometimes on parts of the epidermis which overlie emergences and teeth 

 of various form and arrangement: as examples may be mentioned, the glandular teeth 

 of the margin of leaf-laminse, e. g. species of Prunus, Salix, &c. ', the various ' glands' 

 of the leaf-organs of the Malpighiae *, and species of Acacia " and many others *. 



FIG. 35.— Transvefse section through a young intemode of 

 Betula alba (375). c—e epidermis ; a respiratory cavity under the 

 stoma J c the cuticle raised from e, by a secretory layer, as far as 

 the entry of the stoma (secretion removed by alcohol). 



Bd, 



• Rauter, I.e. p. 30. = Meyen, Secretionsorg. Taf.VI. 7-12. 

 ° Compare TreviranuB, Physiologie, II. p. 6. 



* A. de Jussieu, Monographie des Malpighiacees, p. 92. 



= Unger, Flora, 1844, P- 7°3> Anat. und Physiol, p. 362. 



° Numerous examples of this have been recently described by Reinke, in Pringsheim's Jahrb. 



10, p. 119 ^Nachtr. Anm.). 



