204 INTERCELLULAR SPACES. 



cell-sap makes its appearance in the cells bordering on the passages : further up and 

 throughout the stem orange-yellow granules, which turn blue with iodine, are also 

 found fixed upon the wall of the cells next the passage. In the limiting cells of 

 young passages of the secondary cortex of Pittosporum Tobira, Mtiller mentions 

 numerous starch grains with a covering of yellow oil. The epithelial cells of the 

 reservoirs in the leaf of Ginkgo, in the stems of many Compositse, e. g. Solidago laevi- 

 gata, contain chlorophyll grains : those which surround the round resin-reservoirs in 

 the leaf of Ardisia crenulata are, with exception of the necessary peculiarities of form, 

 in no way different from those of the rest of the chlorophyll parenchyma, to which 

 they belong. 



In many plants which secrete resin (Coniferae, Anacardiacese, Umbelliferae, Ara- 

 liaceae, Compositae) Miiller has by staining with Alkanna found drops of resin not 

 only in the cells bordering on the reservoirs, but distributed widely in the surrounding 

 tissues. Without wishing in the least to combat the correctness of these observations, 

 I regard further careful investigation of the contents of these cells as the more 

 desirable, since very thin sections, which Miiller states that he used . almost 

 exclusively, are not the most suitable preparations for the study of protoplasm and 

 cell contents. 



The contents of the intercellular secretory reservoirs form in most cases a homo- 

 geneous fluid mass, or an emulsion-like mixture without characteristic peculiarities of 

 structure. Their chemical properties are indicated approximately, and for the present 

 sufficiently, by the names above used. The red secretion in the cavities of species of 

 Lysimachia and Myrsineee, which, from its solubility in alcohol, may, till further in- 

 vestigated, be classed with the resins, is an exception to this rule, since it appears in 

 a fixed form, and with apparently crystalline structure, as will be described below. 

 The same seems to be the case, judging from incomplete investigation, in many 

 species of Oxalis. 



The large mucilage-passages, ^mm ^ide, of the Opuntias are characterised by 

 containing numerous and large crystals of calcium oxalate embedded in mucilage. 

 As regards the material characters of the milky contents of the passages of Mamillaria 

 angularis, and its allies, which will be more accurately described below, I have come 

 to no certain conclusion. 



The mode of development of the intercellular secretory reservoirs is for the lysi- 

 genetic forms generally as follows : that, in a group of delicate cells, which arise by 

 definite meristematic divisions, and which correspond in form and arrangement to the 

 future reservoir, the secretion appears at the expense of the original protoplasmic body, 

 and that subsequently the walls of the cells are dissolved, and the separate secretory 

 masses coalesce. Of reservoirs of this category, containing gum and mucilage, only 

 the passages of the periphery of the petiole of the Marattiacese have as yet been 

 carefully investigated, and in their case it is shown, that the elements of the simple 

 row of cells corresponding to the subsequent cavity of the passage are filled with the 

 secretion before they are broken up. Nothing is known of the form in which they 

 first appear. In the investigated reservoirs of ethereal oil and resin the secretion first 

 appears as small drops in the protoplasm of the cells about to be broken down. 

 These increase quickly in size and number, and coalesce after the disappearance of 

 the walls, to larger masses. Where the original cellular body consists of several 



