lOO CELLULAR TISSUE. 



bladder-like glandular hairs. This fact, besides the other points of agreement, shows 

 how nearly the two structures are allied. In Gymnogramme I always found the crys- 

 talline covering seated only on the smooth cuticle of the apical cell. On young, as 

 yet unfolded, fresh leaves of Auriculas, the apical cell of the hair has often a typical 

 bladder-like glandular structure : so that the cuticle which surrounds the resinous 

 secretion is extremely thin, and the apical cell bears occasionally one large resin- 

 bladder, usually two or several small ones. On older leaves I did not observe these 

 bladders : those which occur on young leaves are replaced after long immersion in 

 W'ater by the above-described crystals. All these phenomena, which require more 

 careful observation, point again to the fact that we have here to deal with a peculiar 

 form of glandular hair and glandular secretion. 



Sect. 21. Darwin, in his 'Insectivorous Plants,' has drawn attention to organs 

 belonging to the epidermis, which in their structure and development are closely 

 allied to the hair structures and dermal glands above described, but are distinguished 

 by the fact that, at least in the closely-observed cases, when subjected to continued 

 chemical or mechanical stimulus, they secrete at their surface a fluid, which holds in 

 solution a free (organic) acid, and a ferment similar in its action to Pepsin. As the 

 result of the interaction of the two dissolved bodies, they are capable of dissolving 

 and digesting albuminoid substances, and the solution of these, as well as of Phos- 

 phates, salts of ammonia, &c., is absorbed by them or — a point which cannot be 

 considered as generally established — by the surrounding tissue. According to this 

 digestive function these organs may be termed Digestive glands. Besides the above 

 solutions there often occurs a rich excretion of mucilage which is sticky, and swells 

 with water, especially in species of Drosera, Drosophyllum, and Pinguicula. This 

 appears in the plants named even independently of stimulus, but in this case the acid 

 reaction and digestive effect are absent. In others the mucilage is not observed. 



The organs in question, and the power conferred by them of digesting animal 

 substance and absorbing it as nourishment, are at present known in the case of the 

 peculiarly-formed leaves of Droseraceas, especially species of Drosera, Drosophyllum, 

 Dioncea, and species of Pinguicula. Other plants also absorb dissolved animal bodies 

 as nourishment by means of their leaves. This is certain in the case of Utricularia, 

 and very probable in that of Aldrovanda, Nepenthes, Sarracenia, &c. They then 

 show corresponding organs, which are probably to be regarded as digestive glands, 

 though they are not at present certainly understood. 



The undoubted or presumptive digestive glands have (when they belong to the 

 epidermis) the position and cellular arrangement either of circumscribed dermal 

 glandular spots, or of hairs or scales. 



They are either situated above the ends of vascular bundles (Drosera, and some- 

 times in Nepenthes) or have no direct relation to these (e. g. Pinguicula, Dionaea). 



Of the allied hair structures, which rise above the epidermal surface, those deli- 

 cate, long-stalked, umbrella-like scales (p. 64) which are found in large numbers on 

 the leaf-surface of the Pinguiculas have already been mentioned. They secrete on 

 their upper surface. The digestive glands on the upper surface of the leaf of Dionaea^ 

 and Aldrovanda are quite short, umbrella-like, stalked, round, multicellular scales, 



' [C. de Candollc, Ref. Bot. Jahiesber. 1876, p. 383, Oct.] 



