PROCEEDINGS OP SOCIETIES. 39 



of leaf, lie cut slices of both carrot and leaf together. Having got 

 the sections in the way, he placed them in a watch-glass with some 

 water, and then put them into the exhausted receiver of an air-pumj) 

 in order to extract every particle of air from them, the presence of 

 which would prevent the staining fluid from thoroughly permeating 

 the object. Having thus obtained sections comj)letely saturated with 

 water, the next thing was to stain them. This was done with hfema- 

 toxylin, which produced the familiar violet tint which was so much 

 less fatiguing to the eye of the observer than carmine. When stained, 

 the most important thing to be done was to keep it permanently for 

 future observation. To do this it was first taken out of the staining 

 fluid and washed in water, and after as much as possible had been 

 allowed to run oif, a little absolute alcohol was poured over it. This 

 was in turn got rid of by drops of oil of cloves. But here a precau- 

 tion must be observed. Directly the oil of cloves was put on, a 

 heavy covering of glass inust be placed over, and it must be left 

 under pressure until it cleared, otherwise it would curl up and be 

 entirely spoilt. 



Its features as an object were certain curious little concretions, 

 called cystoliths, lodged in some of the cells, and the question was, 

 what were these ? If the leaf section were examined, it would be seen 

 that immediately below the surface of the leaf was a row of small cells, 

 known as the epidermic cells. Beneath these were two sets of larger 

 cells, the continuity of which was interrupted occasionally to give 

 place to a very much larger cell, which extended deeper down into the 

 softer tissue of the leaf. This was the cell which contained the little 

 ci/stoliths, which were found suspended by a kind of peduncle from the 

 ujiper end of the cell (diagram di*awn and explained). There were, of 

 course, other kinds of cells in the leaf, but it would not be necessary 

 then to take them into consideration. The question was, what were 

 these little concretions ? Were they really composed of crystals of 

 lime, or were they merely of organic nature ? The first idea about 

 them seemed to have been expressed by Meyen, in 1827. He con- 

 sidered that the stem was composed of cellulose, and that the cystolith 

 was composed of gum covered over with crystals of carbonate of lime. 

 Another idea was that it was a concretion formed at the base of an 

 abortive hair. He thought, however, that there was some doubt as to 

 its being a concretion at all, composed of lime salts. He was rather 

 inclined to look upon it as being an organic concretion of a gum-like 

 nature, and for these reasons : — 1. Because when a thin section was 

 made and was looked at in water, it was seen to be highly refractile ; 

 but in about twenty-four hours the whole of this brilliancy dis- 

 appeared, and it looked just like a mass of gum. 2. Because, if the 

 process of staining were prolonged, the entire substance of it would 

 become intensely stained. And 3. Because it did not show any appreci- 

 able power of double refraction when examined in polarized light. 

 He had not tested it with acid, so could not say if any action was 

 produced upon it in that way. He thought that, for these reasons, 

 the cystoliths might be regarded as being composed of cellulose, or of 

 some gum-like material deposited upon a cellulose stem. As regarded 



