SECRETIONS. 



179 



a large quantity of exceedingly fine granules of carbonate of lime, so that the whole 

 represents a mass of stony hardness, from which the calcium salt may be dissolved 

 out by weak acids, with the formation of carbon dioxide gas. Among the lower 

 Cryptogams also cases of calcification are found — i.e. deposits of calcium 

 carbonate in the substance of the cell wall — so that the whole plant is of stony 

 hardness, as in the Corallinese and Melobesiaceae among the Florideae, and even in 

 single species of Halymeda, as well as in Acetabular ia among the Siphoneae 

 (Coeloblastse). 



If we now turn to those receptacles for secretions which contain fluids, we find 

 the contents in the form of gummy mucus, or of latex- like emulsions, which may flow 

 out in abundance on wounding, or of 

 solutions of tannin, balsams and the like. 

 We here meet with tissue-formations 

 which, at the one extreme, pass almost 

 imperceptibly into segmented latioiferous 

 vessels, as in the so-called tannin-bear- 

 ing laticiferous vessels of many Aroidea 

 and species of Musa ; while the other 

 extreme is exhibited in the occurrence 

 of roundish cells, scarcely differing from 

 the surrounding parenchyma, and iso- 

 lated or grouped in all kinds of ways, 

 in which the substances mentioned are 

 contained, usually as mixtures. We may 

 term these structures collectively secre- 

 tion-vesicles, and speak in more special 

 cases of gum-vesicles, resin-vesicles, 

 latex-vesicles, tannin-vesicles, and so 

 forth. By this means the characteris- 

 tic constituents of the contents are in- 

 dicated. Apart from the laticiferous 

 vessels of the Aroidea and species of 

 Musa, from their nature still somewhat 

 doubtful, there are found in the most 

 various subdivisions of the Monocoty- 

 ledons, Dicotyledons, and some Ferns, 

 secretion-vesicles which are formed of thin-walled more or less long, often very 

 long tubular cells, standing one over the other in rows, and accompanying the 

 vascular bundles on the outer side, or at the circumference of the pith : or, as is 

 the case with the rows of vesicles in Phaseolus, running in the soft bast of the 

 vascular bundle itself. Among the most remarkable forms belonging here are 

 the vesicles abounding in tannin which run in the internodes of Sambucus nigra 

 both in the cortex and in the circumference of the pith ; these, according to 

 De Bary, probably extend through the entire length of an internode (20 c. m.), 

 and are at the same time remarkable for their breadth (o-i mm. and more). The 

 so-called utricular vessels also, occurring in the Leeks, and especially in the bulb 



Fig. 179. — Cystolith If c) in a cell of the hypoderm (A) of the 

 upper sidsoftiieleaf of Fi'ciiseittsiica. f epidermis; cA chlorophyll- 

 tissue. 



