DIG 



[ 135] 



DID 



direction parallel to their axis, 

 while they appear of a brownish 

 colour, when viewed in a direction 

 perpendicular to this axis. Leon- 

 hard named this mineral Cordierite, 

 after Cordier, but Cordier himself 

 gave it the name of Dichroite.) A 

 mineral, called also iolite. The 

 prismatic quartz of Mohs; iolithe 

 of Haiiy. Dichroite is of a blue 

 colour, shining lustre, and con- 

 choidal fracture. It consists of 

 nearly 50 per cent, of silica, alu- 

 mina 30, magnesia 11, oxide of 

 iron 5, with a trace of oxide of 

 manganese. It occurs in granite 

 and gneiss. 



DICO'CCOTJS. (from fil? and KOKKOS, Gr.) 

 A capsule which consists of two 

 cohering grains, or cells, with one 

 seed in each. 



DICOTYLE'DON. (from l<t and Korv\rj- 

 wy.) A plant that has two coty- 

 ledons or seminal leaves. 



DICOTYLE'DONOUS. Every plant the 

 embryo of whose seed is made up 

 of two lobes, or which possesses 

 two cotyledons, or seminal leaves, 

 is included in this great division 

 of the vegetable kingdom ; or is a 

 dicotyledonous plant. The stems 

 of dicotyledonous plants are all 

 exogenous, that is, they increase 

 externally by the addition of con- 

 centric layers from without ; these 

 concentric additions being made 

 annually, a vertical section of a 

 tree of this division will show, at 

 once, its age ; the number of rings 

 or circles marking its number of 

 years. Dicotyledonous plants may 

 always be distinguished from mono- 

 cotyledonous by their leaves : mono- 

 cotyledonous plants have the veins 

 of their leaves parallel and not 

 reticulated, while all dicotyledonous 

 plants have the veins of their leaves 

 reticulated. 



DICTYO'GENJE. An order of plants, 

 belonging to the class Exogens, 

 comprising the yam and smilax. 



DIDA'CTYLE. (&<5a/eTvXo9, Gr.) An 



animal having two toes only. 



DIDA'CTYLOTJS. Two-toed; having two 

 toes only. 



DIDE'LPHIS. | (from &V and e\0vs, 



DIDE'LPHYS. j Greek, having two 

 wombs.) A genus of animals, 

 belonging to the class Mammalia, 

 order Terse. All the animals of 

 this genus are marsupial, that 

 is, possess an external abdominal 

 pouch, marsupium, or sac, in which 

 the foetus is placed after a very 

 short period of uterine gestation, 

 and where it remains suspended 

 to the nipple by its mouth, until 

 sufficiently matured to come forth 

 to the external air. The opossum 

 and kangaroo are examples. The 

 didelphys afford the only known 

 example of mammalian remains in 

 the secondary formations. 



DIDE'LPHOID. Belonging to the genus 

 didelphys. 



DIDY'MIUM. One of the sixty simple 

 or elementary bodies. Its symbol 

 is D. 



DIDYNA'MIA. (from &? and Svvajus, 

 Gr.) The name given to the 14th 

 class in Linnaeus' s artificial arrange- 

 ment : it has four stamens, two 

 long and two short. This class is 

 easily distinguished from the 4th 

 class, Tetrandria, which has also 

 four stamens. The flowers of this 

 class are generally labiate ; corolla 

 monopetalous. It is divided into 

 two orders : Gymnospermia, with 

 four naked seeds in the bottom of 

 the calyx, and Angiospermia, the 

 seeds numerous and contained in a 

 seed-vessel. In the first order, 

 with the naked seeds, the plants 

 are mostly aromatic and wholesome, 

 including the mint, lavender, &c. 

 In the second, where the seeds are 

 contained in a seed-vessel, we find 

 digitalis, and other poisonous plants. 



DIDYNA'MIC. ] Belonging to the class 



DIDYNA'MOTTS. j Didynamia. Plants 

 having four stamens, two of which 

 are shorter than the others, are 

 called didynamous. 



