A STUDY IN PLANT VARIATION 249 



Cell Contents and Glandular Stntctures 



1 . Calcium oxalate is excreted into cells of this plant as a waste pro- 

 duct in considerable abundance. The evidence of it is shown by the 

 rosette aggregate of crystals found in different parts of the plant. They 

 are of various sizes and usually occupy an entire cell. The greatest 

 abundance of them is found in the cortex of the stem, and in the loose 

 parenchyma cells of the leaf mesophyll, where they are irregularly scat- 

 tered throughout. Likewise, they are found in the sepals and receptac- 

 ular tube. Again in the fruit, they are found not only in the soft pulpy 

 cells and in the cells which are thickening their walls to form the stone, 

 but also in the developing embryo inside. That they may be found in 

 other parts of the plants is, in the opinion of the writer, very probable, 

 as no special attempt was made to study them, their presence simply 

 being noted in the histological study of the above named parts. 



2. Mucilage is likewise excreted in great abundance, evidence of 

 which is found in the cells of the upper and of the lower epidermis of the 

 leaf. Mucilage canals are also found in the fleshy part of the fruit, 

 and when the fruits are stung by the plum weevil masses of the mucilage 

 exude from the puncture which soon hardens into a plug heaUng up 

 the wound. When the ripe fruits are plucked from the stalks Macfar- 

 lane (18, p. 226) refers to the considerable amount of "bleeding" which 

 occurs when they are heaped in a basket or on a dish for a few hours. 

 This secretion, which is sticky to the touch, is evidently the same mucilage 

 as that previously referred to. If the stalk is plucked with the fruits 

 this bleeding is entirely prevented. Frequently when a branch is broken 

 from the bush or an injury to the bark occurs, mucilage is exuded to 

 cover the exposed wound. 



3. Tannin which gives to the fruits their bitter astringent taste 

 is deposited in a layer beneath the skin. The yellow varieties are almost 

 free from it, while the late maturing ones contain the most; the small 

 purple being extremely bitter. The intermediate types vary in tannin 

 content. The softer and larger varieties when ripe contain only small 

 traces of tannin. 



4. Glands of the most interesting character are found on various 

 parts of the plant, viz., at the junction of the lamina with the petiole, 

 on the lobes of the deciduous stipules and on the teeth of the lamina. 

 These are all fairly large — visible to the unaided eye — of a dark brown 

 color, and very dense. The glands at the junction of the lamina with 

 the petiole are borne on short stalks. Normally, there are two — one 

 on each side of the petiole — but frequently one of these may be absent, 

 while very rarely leaves are found with no glands developed. The 



