GLANDS. 



[ 356 ] 



GLANDS. 



a cellular parenchyma containiug numerous 

 closed follicles like tbe last. 



5. The thymus gland, in which aggre- 

 gated glandular vesicles open into a com- 

 mon closed canal or wide space. 



The glands are further noticed under 

 their respective heads. 



BiBL. Kolliker, Mik. An., and Gew('be- 

 lehre ; Henle, AUg. An. ; ^^^ag•ner, Handw. 

 Phys. ; Todd and Bowman, Phys. Anat. ; 

 Carpenter, Physiol. ; Frey, Histol. 374. 



GLANDS OF Plants.— The glands of 

 plants are special structures formed of cel- 

 lular tissue, in which are produced secretions 

 of various kinds, such as oils, resins, &c. 

 They are ordinarily more or less closely 

 connected with the epidermal tissues, but 

 not in all cases, the latter instances forming 

 a kind of transition to the receptacles of 

 special secretions, turpentine-reservoirs &c., 

 found in the interior of the stems of many 

 plants. Glands may be conveniently divided 

 into external and internal : the former are 

 sessile, or stalked (when thsy present the 

 character of grandular hairs., of variou,-; 

 forms) ; while the latter are generally visible 

 externally as transparent dots scattered 

 over an organ, such as a leaf, giving it the 

 appearance of having been pricked all over 

 with a pin ; when of more considerable 

 dimensions, and with thicker walls, they 

 produce tuberculation of the surface, as on 

 the rind of the orange, &c. 



E.rternalylands. These may besubdivided 

 into simple and compound. 



Simple e.vternal (/lands are either sessile 

 vesicles or hairs, composed of a single vesi- 

 cular or elongated epidermal cell filled with 

 secretion; or they are hairs composed of a 

 simple row of cells, one or more of which 

 are filled with secretion. Examples of this 

 may be found in the epidermis of Priinida 

 sinensis, Gilia tricolor, Erodiiun cicviarinm, 

 Achimenes (Bl. 28. fig. ,32), Stachys, Marru- 

 hium, Digitalis jmrjnirea (fig. 33), Antir- 

 rhinum omijus (fig. 34), (Enothcra, llcUe- 

 bor us fat id us, Scropliularia nodosa (fig. 41), 

 Sempervivum, Salvia, Thymus, Mellissa, 

 Me.<icmb-yanthemum, Garden Chrysanthe- 

 mum (fig. 30), &c. 



The slings of the nettles ai-e to be placed 

 here; they consist of very long, tapering, 

 single hairs, with an obtuse point, and a 

 bulb-like expansion at the base, imbedded 

 in a dense layer of epidermal tissue (1*1. 28. 

 fio-. 8). The hair is filled with the poisonous 

 secretion. When the point touches tlie 

 skin, it breaks ofi" and allows the escape of 



the fluid contents, which are squeezed out 

 by the pressure, and probably by the tension 

 of the tissue around the bulb. 



Compound external glands difier from the 

 simple only in the fact that they are coin- 

 posed of a greater or a smaller number of 

 cells combined into a mass, usually of sphe- 

 rical or allied form. They may be sessile, 

 or stalked upon a simple or compound hair. 

 Examples of sessile form occur in Dictamnus 

 albiis (PI. 28. figs. 38, 30), Rohinia viscosa, 

 the leaf of the mulberry and the Hop 

 (fig. 14), and the stipular glands of Cin- 

 chona, Galium, &c. ; of the stalked, in the 

 Rose (fig. 46), species of Huhiis, Drosera, 

 and on many aromatic or viscid plants. 



Internal glands. These consist of cavities 

 in the subepidermal tissue, of variable size, 

 bounded by a firm layer of cells, and filled 

 with oily or resinous secretions. They ap- 

 pear to be formed either of one cell, when 

 small, or, when large, of a definite mass of 

 cells, which, after the production of the 

 secretion, have their Avails obliterated so as 

 to form a large chamber ; possibly, however, 

 some may be intercellular spaces into which 

 the secretion is poured out. Examples of 

 moderate dimensions are found in the leaves 

 of Dictainnus, 3Iagnolia (PI. 28. fig. 12), 

 Hypericum perforatum, and other species, 

 Myrtacece, Puta graveolens (fig. 11), &c. 

 Very large glands of this kind contain the 

 oil in the rind of the orange (fig. 280) and 

 other species of Citrus. 



Fig. 280. 



"-(^ 





Section of the rind of an orange, showing the internal 

 glands, R, R. 



Magn. 50 diams. 



The nectaries of flowers have their tissue 

 metamorphosed into a condition resembling 

 that of the secreting part of glands ; and 

 the hairs of the stigma of Flowering Plants 

 produce a secretion at the period of impreg- 

 nation. Brongniart has lately pointed out 

 the existence of internal glands in the dis- 

 sepiments of the ovaries of the petaloid 

 Monocotyledons. These structures form a 

 transition to the turpentine-canals &c. of 

 the Conifer;©. (See Secreting organs 

 of I'lants.) The Gummi-Keiden of Meyen 



