136 SECRETORY RESERVOIRS. 



excreted. Direct observation teaches us the same of the mucilage, resins, and ethereal 

 oils of the dermal-glands. The fact is no less evident that the resins, mucilages, &c,, 

 which are laid by in circumscribed reservoirs, e.g. in the resin-sacs of the Laurineae, 

 Piperaceae, Zingiberacese, &c., after they begin to be secreted in the meristem, remain, 

 like the calcium oxalate, laid by without further use. 



In accordance with all these facts we are bound to regard the whole series of 

 the bodies in question, like the secretions of the dermal-glands, as bodies excluded 

 from the constructive metastasis, and to term them, together with these, Secretions. 

 Their occurrence as admixtures of the contents, or as constituents of the membrane 

 of active cells, which may be proved for all bodies of this category, is no argument 

 against this generalisation, since on the one hand calcium oxalate shows plainly that 

 one and the same body may be excreted both in small quantity in an assimilating 

 cell, and in large mass in a special reservoir ; on the other hand, in the uncertainty 

 of our present knowledge, a fundamental difference is always possible between what 

 is in the one and in the other case termed, for instance, resin. And finally, this 

 view does not affect that of the application of the secretion to some further uses by 

 the plant, as, for instance, in the well-known case of the hairs on buds. 



On these grounds we group the whole of the above-described reservoirs together 

 as secretory-reservoirs. There may be distinguished reservoirs of crystals, mucilage, 

 r-esin, &c., according to their exclusive or preponderating contents. Since resin 

 and ethereal oil occur usually as mixtures, and rarely separate, and since we cannot 

 here enter upon chemical details, which are often uncertain, we shall in the sequel 

 use the words reservoirs of resin, oil, and balsam without claim to exact indication of 

 contents, and usually in connection with the meaning customary for each special 

 case. The term gum-resin is used to indicate, but with still smaller claim to accu- 

 racy, the mixture of watery and resinous secretions, which is milky when fresh. 

 According to their structure the reservoirs may be distinguished as Sacs, i.e. struc- 

 tures derived from cells, which retain their walls, and are therefore usually termed 

 cells ; and intercellular cavities, which according to their form are termed either 

 passages or gaps. For many of these forms, which vary in structure and contents, the 

 term glands, or internal glands, is in use. It will be difficult to banish it, since it has 

 established itself in the incorrigible terminology of Systematic Botany, although, as 

 the sequel will show, it is not at all wanted. If it is to be retained, it ought accu- 

 rately to be used for all secretory-reservoirs, any other use of it is purely arbitrary 

 and conventional. 



With those which certainly belong to this category, we must connect many 

 doubtful structures, such as many ' tannin sacs,' the ' vesicular vessels ' of the species 

 of Leek, and others to be named below : this classification may be corrected when 

 more exact observations have been made. 



We have already drawn attention to the alternative occurrence of the different 

 forms of secretory reservoirs, in different members of the same plant, or in different 

 genera, or larger circles of affinity. 



Similar alternative relations occur here and there between reservoirs and latici- 

 ferous tubes (comp. Chap. VI). Even if one discounts the Aroideae and Musacese, 

 the laticiferous tubes of which should perhaps be enumerated in the present chapter, 

 the fact is certain that internal secretory reservoirs are absent from all plants which. 



