SECTIONS. 



688 ] 



SEEDS. 



they render it possible to determine the 

 genus by their arrangement. In Pimis they 

 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 meduDary ravs are 

 likewise 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 vascu- 

 lar 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-reser- 

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

 thoroughly studied. The resin- and oil- 

 canals of the Umbellifer^ are of 



great im- 

 portance ; but the former, chiefly occurring 

 in the roots, are imperfectly known. The 

 oil-ieservoir of the fruits (vitfes) consists of 

 elongated excavations in the cellular tissue, 

 filled with oil. Canals containing odorife- 

 rous oils occur in some of the Compositas. 

 Besin-canals occur also in the common lime. 

 Gum-canals, consisting of simple or 

 branched intercellular passages with a spe- 

 cial coat of small secreting cells, occm- in 

 the leaf-stalks of Cycadacese, the bark of 

 the Amygdaleee, the stems of the Malvaceae, 

 Cactaceae, &c. Structm-es of similar nature 

 contain the milky juices of certain plants, as 

 the Anacardiaceae ; and these appear to be 

 different from the ordinary Latex vessels. 



BiBL. Meyen, Secret.-Organe d. Pflanzcn, 

 1837, 18 ; Unger, An. und Phys. der Pflcm- 

 zen, 1855, 204 ; v. Tieghem, An. Sc. Nat. 

 1872, xvi.; Sachs, JSoi. 79. 



SECTIONS. See Preparation; and 

 for Schiefferdecker's section-cutter, Schidtze's 

 Arch. 1876, xii. 91 ; a modification. Kiddy, 

 Qu. Mic. Jn. 1877, xvii. 35 ; and Lewis, 

 M. M. Jn. xvii. 300. 



SEEDS. — These are interesting objects j 

 for microscopic examination in respect to 

 many difiereut characteristics. Among ^ 

 them may be mentioned first the variety of 

 beautiful markings upon the surface, which ; 

 render almost all saeds, like the elytra of j 

 beetles, interesting opaque objects for ob- 

 servation with a low power. A few striking { 

 forms are represented in Plate 89. figs. 14- 

 18 ; and we give a list of kinds easily to be j 

 obtained. , 



j Hypericum. 

 ' Lychnis. 



Stellaria. 



Reseda. 



Lepidium. 



^'igella. 



Erica. 



Anayallis. 



Orobanche. 



Linaria. 



CMronia. 



Oentiana. 



Datura. 

 Nicotiana. 

 Petimia. 

 Sedum. 

 Saxifraga. 

 Capparis. 

 Elatine. 

 Gesnera. 

 Begonia. 

 Delphinium. 

 Scrophularia. 



Maurundya. 



Sphenogyna. 



Hyoscyamvs. 



Setnpervivum. 



Limnocharis. 



Silene (PI. 39. 



figs. 16, 17). 

 Dianthus (PI. 39. 



fig. 15). 

 Papaver (PI. 39. 



fi^. 14). 



Antirrhinum. Digitalis (PI. 39, 



Mesembryanthemum. fig. 18). 



The following are well seen when mounted 

 as transparent objects in Canada balsam. 



Parnassia. 



Drosera. 



Orchis. 



Pyrola, 



Monotropa. 

 Hydrangea, 



Saxifraga. 

 Rhododendron . 



j The testa or outer skin of some of the 

 latter (also Begonia), when removed from 

 j the seed and viewed with a high power, ex- 

 i hibits elegant pitted cells. The surface of 

 the seed of Cobcea is mealy with little scales 

 consisting of p^Tiform cells containino- a 

 spii-al fibre (PI. 28. fig. 20). 



The surface of various seeds, such as Cnl- 

 lomia and Puellia, and the pericarp of many 

 seed-like fruits, such as that of Salvia and 

 Senecio, present remarkable Hairs. 



The stones of plums or cherries, the so- 

 called shell of the Cocoa-nut and similar 

 fruits, exhibit remarkably thick Secondary 



DEPOSITS. 



The examination of the structure of ripe 

 seeds is a matter of great importance in 

 botany. The investigation will vaiy much 

 according to circumstances, ^^'here seeds 

 are large, the microscope is only required 

 for the examination of their tissues; but 

 small seeds must be examined by dissection 

 with needles under the simple microscope, 

 or by sections, which are most easily made 

 by fixing the softened seed into a piece of 

 wax. Seeds have two coats, the testa and 

 tegmen, or external and internal membrane, 

 and, according as the seed is or is not albu- 

 minous, an albumen enclosing the embiTO, 

 or an embryo of larger size immediately 

 invested by the coats. The characters of 

 the Albumen and Embryo will be foimd 

 under these heads, as also other particulars 

 under Ovule. Embryos are either Mono- 

 cotyledonous or Dicotyledonous ; sometimes, 

 however, the two cotyledons are soldered 

 together more or less completely. In the 

 Conifer?e and certain genera of Dicotyle- 



