SECRETING ORGANS. 



[ 572 ] 



SEEDS. 



layers differs again, bein^ usually more 

 sparing in quantity, but very firm and elastic, 

 and strongly resisting decomposing agents ; 

 the composition appears to be of that modi- 

 fication of cellulose called suberine. 



BiBL. Gen. WorJcs on Structural Botany; 

 Mohl, Vegetable Cell, London, 1852. p. 10, 

 Botan. Zeit. p. 97 (1847) (Transl. in Tay- 

 lor^s Scientific Memoirs, 2nd ser. i. p. 95) ; 

 Schacht, Pflanzenzelle, Berlin, 1852 ; Crii- 

 ger, Bot. Zeit. xiii. p. 601. 1855; Trecul, 

 Ann. des Sc. nat. 4 ser. ii. p. 273 ; Wigand, 

 Intercellular-substanz u. Cuticula, Bruns- 

 wick, 1850; Miilder, Phys. Chemistry, Edin- 

 burgh, 1849, p. 347. 



SECRETING ORGANS, of Plants ; 

 Reservoirs or Receptacles for Se- 

 cretions. — The structures falling under 

 this head have been in part treated under 

 the heads of Glands and Laticiferous 

 Tissue, but there still remain certain 

 organs of analogous character, which could 

 not be properly included under either of the 

 above. The name of receptacle or reservoir 

 for peculiar secretions is ordinarily applied 

 to groups of cells, of variable, but most fre- 

 quently elongated prismatic form, contain- 

 ing special secretions, either in their cavities 

 or effused into their intercellular passages, 

 traversing in the form of cords or bundles the 

 parenchymatous or prosenchymatous tissues. 

 They are almost special characteristics of 

 families, and by no means frequent ; the 

 Coniferse, the Cycadaceae, the Aloineous Li- 

 liacese, the Polygonacece, Composita3, Um- 

 belliferae, Amygdaleous Rosaceae, Legumi- 

 nosse, &c., afford striking examples. 



In the Coniferse the turpentine-reservoirs 

 are very remarkable, and to a certain extent 

 they render it possible to determine the 

 genus by their arrangement. In Pinus tliey 

 consist of bundles of elongated, thin-walled 

 cells, running through the wood parallel to 

 the axis of the stem. These thin-wall cells 

 are densely filled with turpentine ; in some 

 cases the cells of the medullary rays are hke- 

 wise filled with turpentine, and, besides 

 these, perpendicular intercellular passages ; 

 the latter form of turpentine-canal is chiefly 

 met with in the bark. Turpentine- canals 

 also exist in the leaves of the Coniferse, the 

 scales of the cones, &c. 



The reservoirs of the Aloes are bundles of 

 prismatic cells accompanying the vascular 

 bundles of the leaves and stems. The 

 colouring matter of the root of rhubarb is 

 contained in cells of imperfect medullary 

 rays. The structure of the balsam-reservoirs 



of the myrrh tree, &c., has not been 

 thoroughly studied. The resin and oil-canals 

 of the Umbelliferse are of great importance, 

 but the former, chiefly occurring in the 

 roots, are imperfectly known. The oil-reser- 

 voir of the fruits {vittce) consists of elongated 

 excavations in the cellular tissue, filled with 

 oil. Canals containing odoriferous oils occur 

 in some of the Compositae. Resin-canals 

 occur also in the common lime. 



Gum-canals, consisting of simple or 

 branched intercellular passages with a special 

 coat of small (secreting?) cells, occur in the 

 leaf-stalks of Cycadaceaj, the bark of the 

 Amygdalece, in the stems of the Malvaceae, 

 Cactaceae, &c. Structures of similar nature 

 contain the milky juices of certain plants, 

 as of the Anacardiaceae, and these appear to 

 be different from the ordinary Latex 

 vessels. 



Bibl. Meyen, Secretions - Organe der 

 Pfianzen, Berlin, 1837. p. 18; Unger, Anat. 

 und Phys. der Pfianzen, 1855. p. 204. 



SECTIONS. See Preparation (p. 

 530). 



SEEDS. — These are interesting objects 

 for microscopic examination in respect to 

 many different characteristics. Among these 

 may be mentioned first the variety of beau- 

 tiful markings upon the surface, which ren- 

 der almost all seeds, like the elytra of bee- 

 tles, interesting opaque objects for observa- 

 tion with a low power. A few striking 

 forms are represented in Plate 31. figs. 14- 

 18, and we give a list of kinds easily to be 

 obtained. 



Hypericum. 

 Lychnis. 

 Si/e/ie(Pl. 31.figs. 



16 & 17). 

 Stellaria. 

 Dianthus (PI. 31. 



fig. 14). 

 Reseda. 

 Papaver (P\. 31. 



fig. 14). 

 Lepidium. 

 Delphinium. 

 Nigella. 

 Erica. 

 Anagallis. 

 Orobanche. 

 Scrophularia. 

 Antirrhinum. 



hinaria. 



Chironia. 



Gentiana. 



Datura. 



Nicotiana. 



Petunia. 



Digitalis (PI. 31. 



fig. 18). 

 Hyoscyamus. 

 Mesembryanthemum. 

 Sempervivum. 

 Sedum. 

 Saxifraga. 

 Limnocharis. 

 Capparis. 

 Elatine. 

 Gesnera. 

 Begonia. 



The following are well seen when mounted 

 as transparent objects in Canada balsam. 



