770 SUMMARY OF OUEEENT EESEAECHES EELATING TO 



without hairs, crevices in the tissue, stomata. The secreting cells, 

 spaces, or passages may contain resin, gum-resin, balsam, or an 

 essential oil. 



Secreting cells are an extremely common cause of transparent 

 dots, and are usually characteristic of whole families or at least of 

 genera. Bound intercellular secreting spaces may be lysigenous, as 

 in Rutaceas, or schizogenous, as in Hypericineas, the two kinds show- 

 ing no difference in the mature condition. Both kinds are of great 

 importance from a systematic point of view, furnishing distinguishing 

 characters for entire families. Thus lysigenous secreting spaces 

 occur in the Rutaceas, Myoporinese, and Leguminosse ; schizogenous 

 are constant in the Hypericinese, Myrsinese, Samydete, and Myrtacese. 

 Intercellular secreting passages of schizogenous origin cause trans- 

 parent lines in a number of Guttiferae, and in some species of 

 Hypericum. 



Epidermal cells in which the inner wall next the parenchyma of 

 the leaf is strongly thickened and mucilaginous cause pellucid dots in 

 a number of families and genera. Cells in the interior of the leaf 

 with all the cell- walls strongly mucilaginous occur in Anonacese and 

 Laurineae, but not in all the species. Cells with mucilage in the 

 interior are found in the Ampelideao, and especially in the American 

 species of Cissus. 



Raphides-cells are of great importance systematically. They 

 are sometimes replaced by cells with single very long prismatic 

 crystals. Transparent dots caused by cystoliths occur in Ficus, 

 Momordica, and some Acanthaceae. 



Of sclerenchymatous elements the most common are spicular 

 cells. Round groups of sclerenchymatous cells also occur, and 

 elongated sclerenchymatous bundles ; but all these forms are of com- 

 paratively small value systematically. Stellately branched scleren- 

 chymatous bundles, the so-called "internal hairs," are constant in 

 Nymphcea and in the genus Ternstrcemia. 



The following are only occasional causes of transparent or pellucid 

 dots, of but little systematic importance : — Depressed pits in some 

 Capparideffi and in Victoria regia ; depressed glands in some Meliaceae ; 

 rupture of the tissue in some Burseraceae, in Nyssa capitata and 

 Placodiscus leptostacliys ; cells with sphaerocrystalline deposits of 

 calcium sulphate, sodium oxalate, or of an organic substance of un- 

 known nature ; the meshes of the network of vascular bundles in some 

 Capparideae and Portulaceae, and finally stomata. 



Secretory System of the Root and Stem.* — In pursuance of 

 previous investigations P. Van Tieghem continues his examination of 

 the structure and position of the secretory system in the following 

 natural orders : — Umbelliferae, Araliaceae, Pittosporeas, Compositae, 

 Clusiaceffi, Hypericaceae, Ternstroemiaceae, Dipterocarpeae, Liquidam- 

 bareae, and Simarubaceae. In the Umbelliferae and Araliaceee the 

 system, which occurs in the roots, tigellum, and cotyledons, is 



* Bull. Soc, Bot. France, xxxi. (1884) pp.'' 29-32, 43-4, 112-6, 141-51, 

 247-5(i. ^f. > 



