144 



SECRETORr RESERVOIRS. 



in groups or rows, usually without any dearly recognisable order. In the tubers of 

 Orchis they appear fairly regularly as wide sacs completely filling the meshes of a 

 network, which is composed of plates of starchy parenchymatous cells, one or more 

 layers thick, which face in all directions \ When lying in water they appear as 

 intercellular cavities filled with swollen mucilage, and were described as such by the 

 older anatomists \ 



If the swelling of the mucilage be prevented, e. g. by treatment with alcohol, the 

 space enclosed by an outer cellulose membrane appears either entirely filled with 

 the firm mass of mucilage, or partially, so as to leave an unimportant central cavity. 

 The mass of mucilage shows in the majority of cases — Malvaceae, Cactaceae ', Laura- 

 cese, — the structure of a very thick, abundantly and deHcately stratified cell-wall; it 

 often has even pits (Malvaceae), and is, as regards its origin and morphological signifi- 

 cance, nothing more than a cell-wall which has thickened strongly at the expense of 

 the internal cavity. According to Trdcul's statements this point may, it is true, be 

 doubted, and new investigations desired. In other cases, and as types of these the 

 tubers of Orchis may be named, the mass of mucilage has no such stratification : it 

 developes from a drop of mucilage, which appears first like a vacuole within the 

 protoplasm, and surrounds a bundle of Raphides lying near to the nucleus : this drop 

 as it grows completely displaces the protoplasm and nucleus, while the bundle of 

 Raphides remains imbedded in the mature mass of rhucilage. The sacs in the cortex 

 of the silver-fir appear to correspond to these in structure, their development remains 

 to be more accurately investigated. 



In later stages of life the sacs often appear swollen up in the living plant to 

 structureless masses (e. g. in Althaea rosea) : these then fill up cavities in the pa- 

 renchyma of various form and size, according as they have been derived from the 

 swelling of one or several sacs. These latter structures may best be connected with 

 those mucilage- containing cavities, originally derived from a group of swollen 

 mucilaginous cells, which are described in the parenchyma of the Lime (cortex, 

 leaves, bud-scales *) : also the ' gum '-bearing cells, and cavities formed by the 

 swelling of these, which were described by Tr^cul * in the parenchyma of the branches 

 of Conocephalous naucleiflorus. This author himself doubts whether the gum- 

 cavities of the species of Quiina described by him * belong to this category, or to the 

 products of secondary disorganisation. Subject to the same doubt, the small masses 

 of mucilage scattered through the parenchyma of the stem and leaf of Welwitschia ' 

 may be mentioned here. 



The sacs with which we are now dealing may be distinguished from those 

 gummy and mucilaginous products of disorganisation which may be derived in a 

 secondary manner from the most various tissues, by their originating directly from 

 the meristem ; they often appear as its iirst recognisable product of differentiation, 



' Frank, I.e. — Berg, Atlas z. pharm. Waarenkunde, Taf. 23. 



' Meyen, Secretionsorgane, Jj. 22. 



= Wigand, in Pringsheim's Jahrb. III. p. 149, Taf. VII. 6. 



* Frank, Beitr. z, Pflanzenpliysiologie, p. 113. 



s Comptes ELendus, torn. LXVI. p. 575 (1868). 



" Ibid, torn: LXIH. p. 717 (1866). 



' Compare Hooker, Welwitschia, pp. n, 19. 



