SECRETIONS OF PLANTS. 



SKDT'M. 



J3! 



principally of Unnic add. This acid is converted into gallic acid by 

 oxidation. Such a process take* place during the formation of the 

 gall* prudured by the puncture of insects in the buds of many of the 

 spsriss of Qnerau, especially Q. iufcrtoria. Thaw excraeoeooe* are 

 called gall-nuts, and from the preeenoe of thu acid in them it has 

 been called gallic acid. [GALLS; QOKRCOs; ACACIA; I'TKRUI-AKI-UA ] 



The alkaloid* are substances found in the leaves, fruits, bark, and 

 other parts of plants. They are some of them peculiar to particular 

 species of plants, whilst others are more generally diffused. Many of 

 them poweas extraordinary properties in relation to the animal king- 

 dom, producing poisonous effect* : such are strychnia, from the 

 SrrycAno* A'kx Vomica; morphia, from the Paparcr tomniferum ; 

 conia, from the Com urn mocWufum. These substances are always 

 found in combination with organic or mineral acids. There ia how- 

 ever another clan of mbsUnces closely resembling these in their 

 composition and action, which do not combine with acids. These are 

 called neutral principle! : inch is theine, the principle found in tea, 

 coffer, and Paraguay tea ; and theobromine, the principle of cocoa. 



The volatile oils are another group of secretions of great interest 

 They dinar in composition and character from the mixed oils, and do 

 not appear to belong to the assimilable secretions. They are many of 

 them used as perfumes others as stimulant medicines, and are 

 remarkable for the interesting compounds they can be broken up into 

 by the agency of chemistry. Their investigation is throwing much 

 light on vegetable chemistry. [OILS.] 



The resins are a group of substances standing in a similar relation 

 to the fixed oils, as the volatile oils. They do not appear to be assimi- 

 lable, they are only occasionally formed, and present special properties 

 in particular plants. They are often combined with gum, forming 

 the substances called gum-resins, and from this combination it may be 

 supposed they are directly formed from the ternary assimilable secre- 

 tions. When occurring with gum, as in the case of the gum-resins of 

 the VmbtUifera, or without gum, as in the resins of the Coniferte and 

 in Myrrh, they are combined with volatile oils, which appears to give 

 them their peculiar odours, flavours, and action. In the Coniferce the 

 volatile oil they are combined with is the same in most species, and 

 is used in the arts under the name of oil or spirits of turpentine. 

 (L'uMi tn.v-j Wax is another substance very commonly found in 

 plants, and having relation with the fixed oils. [WAX.] Caoutchouc 

 and Qutta-Percha are also compounds belonging to the non-assimi- 

 lable group of vegetable secretions, and are remarkable for the absence 

 of either oxygen or nitrogen. [INDIA RUBBER ; ISONAXDHA.] 



Although the processes by which these products may be gradually 

 elaborated in the vegetable kingdom may be-very numerous and much 

 more complicated than any processes with which we are at present 

 acquainted, we can readily explain their formation from the carbonic 

 acid, water, and ammonia, taken up by plants, and the loss of oxygen. 



The following tables illustrate this process, with regard to several 

 of the substances mentioned : 



TABLE Or SUBSTANCES FORMED FROM CARBONIC ACID AND WATER, 

 BT THE LOSS OF OXYOEN. 



TAIILI Or SUBSTANCES FORMED FROM CARBONIC ACID, AMMONIA, 

 AND WATER, BT THE LOSS OF OXYGEN. 



It should not however bo lost sight of that other element* besides 

 the four organic are constantly found present in the secretions of 

 plants. Sulphur and phosphorus are found in fibrine, caseine, and 

 albumen. The alkalies and alkaline earths are found very commonly 

 associated with all these accretions, and it U very certain that plants 

 will not form their secretions unless the inorganic elements are 

 present. [SAP ; ROOT.] 



SECRETIONS, VEGETABLE. [SECRETIONS OP PLANTS.] 

 SECUNDIXES. [ItoRODfcrioN IN PLANTS AND ANIMALS.] 

 SECURl'FERA, a family of Hymenoptorous Insects of the section 

 Terebrantia, the species of which are chiefly distinguished by their 

 having the abdomen senile, or joined to the thorax so as to appear a 

 contiuuation of that part, and not separated by a slender peduncle. 

 In the females, the abdomen is provided with a saw-like apparatus, 

 which not only serves for depositing the eggs, but for preparing a 

 place fur their reception. The larva: greatly resemble those of lepid- 

 opterous insects, and, like them, feed upon plants ; they are cylin- 

 drical, soft, and fleshy; have the head vertical, and the three thoracic 

 segments each provided with a pair of legs ; besides these, the abdomen 

 is often provided with pro-legs. 



The Seeuriftra are divided by Latreille into two sections, the 

 Tenthredintta and the I'roccrata. The first corresponds with the 

 genus Tcnthrcdo of Linnicus, the species of which have thu mandibles 

 elongated and compressed ; the maxillary palpi are six-jointed, and the 

 labial have four joiuts; the four wings are always divided by the 

 nervures into numerous cells. The abdomen is composed of nine 

 segment*, the last of which is provided with an oviduct composed to 

 two serrated lamella: ; these are pointed and lodged between two 

 others forming a kind of sheath. By means of this saw-like ovipositor 

 the female Tenthredo bores holes in the stems and other parts of plants, 

 in which she deposits her eggs. In each hole, after the egg or eggs are 

 deposited, a liquid is injected, the use of which, it is supposed, is to 

 prevent the closing of the opening. The wounds thus made . increase 

 in volume, and form excrescence*, which are cither hard, or soft and 

 pulpy, according to the nature of the plant or of the part wouuded. 

 These tumours then form the domicile of the larvae, which inhabit them 

 either solitarily or in society, and in them undergo their metamor- 

 phosis. Generally however the larva; of the TenlAraiinufrr live exposed 

 on the leaves of the plants upon which they feed, and these larvae are 

 usually observed with the body more or less rolled in a spiral manner. 

 Wheu about to assume the pupa state, they inclose themselves in a 

 cocoon which is sometimes fixed to the plant, but frequently they bury 

 themselves in the ground previously to assuming the pupa state. 



The second section (l.'rocerata) is distinguished from the preceding 

 by the mandibles being short and stout, the ligula entire ; the ovi- 

 positor of the females is sometimes exserted and composed of three 

 slender appendages, and sometimes spirally rolled within the abdumeu. 

 It is composed chiefly of the Liunaean gcuui Stre.c. 

 SEDGE. [CLADIUM; CAREX.] 

 SEDGE-WARBLERS. [STLVIADA] 

 SEDGES. [Cri-ERACE*.] 



SEDUM, a genus of Plants belonging to the natural order Cnutu- 

 lacecc. It is known by possessing a 5 ported calyx with ovate usually 

 turgid leaf-shaped sepals ; five petals, which are usually spreading ; 

 ten stamen*, an hypogyuous scale at the base of each carpel; fivo 

 carpels. They are mostly herbs or shrubby plant*, with stems 

 usually branched from the base. The flowerless stems are crowded 

 with It-ares, which are alternate, seldom opposite, fleshy, terete or flat, 

 and entire. The flowers are commonly yellow, sometimes white or 

 blue, and are arrayed in cymes. The species of Saturn are inhabit- 

 ants of the temperate and warmer parts of the earth, aud are mostly 

 found in dry, barren, rocky, or arid situations where nothing else will 

 grow. Their roots appear to serve only the purpose of holding tin -m 

 in the ground, whilst their leaves ate so constructed that they absorb 

 moisture from the air, and prevent its being again evaporated. 



& Khwliola, Rose-Root Stonecrop, or Rhodiola, Leaves flat, oblong, 

 serrated at the apex, glabrous, glaucous ; root tuberous ; stems single ; 

 flowers with 4 petals, 8 anthers, and dioocious from abortion. It is a 

 native of mountainous districts of the middle of Europe, of Siberia, 

 and north America. In Great Britain it is found on mountains in thu 

 north of England, Scotland, and Wales. It is a glaucous plant with 

 yellow flowers. The root, when dried, has a sweet taste and smell, 

 aud hence its common name. The leaves have been used as a cata- 

 plasm in headache, and the root has been supposed to possess anti- 

 scorbutic qualities. In Greenland it is eaten as a salad. This and some 

 allied species constituted the genus Rhodiola, but the difference between 

 them and .Sn/um does not justify the separation. 



S. Tilcji/iium, Orpine, or Tuberous Stonecrop. Leaves oblong or 

 oval, attenuated at the bale, flat, toothed, glabrous; stems erect; 

 cymes corymbose, terminal ; stamens equal in number with the petals. 

 It is found on rocks, walls, aud dry stony places in most .parts of 

 Europe : in Great Britain it is met with on the borders of fields, in 

 hedges and bushy places, on a gravelly or chalky soil. Several 

 varieties have been described, and sometimes as species. The most 

 frequent is one with purple flowers, S. T. purpureum. The leaves of 

 this plant are sometimes eaten as a salad ; and in former times the roots 

 were in request us a remedy in haemorrhoids aud other diseases. 

 & Anacairpseri'i, Anacatnpaeros, or Evergreen Orpine. Leaves 



