SACS CONTAINING CRVSTALS. 1 ^y 



are provided with laticiferous tubes. In the group of Artocarpeae, which in common 

 with the majority of its aUies is provided with laticiferous tubes, these are absent, 

 according to Trdcul, in Conocephalus naucleiflorus, while in their place this plant has 

 mucilage-containing sacs and cavities. Among those Compositae, which have been 

 investigated, the Cichoracese are distinguished from the rest by their having lati- 

 ciferous tubes, and by the absence of the oil-ducts present in the others : only in 

 Scolymus are both organs developed. 



Further, it is often impossible to ignore an alternative relation between the occur- 

 rence of dermal-glands and internal secretory-reservoirs. In the Cycadese, Coniferag, 

 Lauraceae, Umbelliferag, Aurantiaceae, and Clusiaceae, which have specially large num- 

 bers of the latter structures, dermal-glands are absent or rare. For other families, 

 e.g. the Labiatae, the converse holds. Exceptions, with both sorts of organs side by 

 side, occur not uncommonly it is true, e.g. Dictamnus, and many Composit^e with 

 glandular hairs and internal reservoirs. And finally, we must not omit to notice 

 that both organs may be altogether absent, as e.g. in the Gramina, Cyperaceae, 

 Palms, many Cruciferae, Ranunculaceae, in Taxus alone of the Coniferae, &c. &c. 



The relations, above brought into prominence, between the different organs 

 which form secretions, should always be kept in view during their consideration, in 

 which the first duty is to separate them according to their structure : we will therefore 

 occupy ourselves first with the sacs containing secretions. The intercellular reser- 

 voirs will be treated of in Chap. VII, and the intermediate structures will be noticed 

 in a fitting place. 



I. Sacs con/ai'm'ng Crystals. 



Sect. 32. It is known that crystals of calcium oxalate are generally distributed 

 as constituents of the cell contents. In certain sacs they almost exclusively fill the 

 internal space, and these may be distinguished as crystal-bearing sacs. The crystals ^ 

 consist, as far as is known, entirely of calcium oxalate, which is crystallised either in 

 the quadratic or klinorhombic system — according to Souchay and Lenssen, when 

 quickly deposited it takes the klinorhombic form, with the composition 



when the crystallisation is slower it forms as quadratoctahedra of the composition 



Cao}^*^«-^-^^^0- 



The fundamental form of the crystals belonging to the quadratic system is the 

 quadratoctahedron, that of the klinorhombic crystals, which are far commoner in 

 plants, is the hendyohedron : derived forms occur of the most various shape, e.g. 

 klinorhombic columns, klinorhombic plates, twin forms, and blunting of corners. As 

 specially common forms, which can hardly be accurately defined crystallographically, 

 may be named the spear- or needle-shaped crystals, elongated and pointed at 

 both ends, which De CandoUe ' has termed Raphides, They belong most probably, 



* See Holzner, Flora, 1S64, pp. 273 and 556. — Ibid. 1866, p. 413. 

 ^ Organographie vegetale, I. p. 126 (pa^js = needle). 



