ELEMENTARY STRUCTURE. 



53 



little transparent spots, which appearance is due to the oily 

 matters thoy contain refracting tlie hght in a different manner 

 to the parts surrounding them. In some instances they are of 

 large size, and project more or less beyond the surface of the 

 epidermis in the form of little tubercles, as on the rind of the 

 Orange {fig. 131), Lemon, Citron, &c. Internal glands are 

 very common in many plants, besides those above mentioned : 

 thus in all the Labiate Plants, as jMint, Marjoram, Thyme, 

 Kosemary, Sage, &c. : and it is to the presence of the secretions 

 they contain that such plants owe their value as articles of 

 domestic economy or as medicinal agents. Lately Brongniart 

 has described what he calls internal glands, in the interior of 

 the ovaries of some Monocotyledons. 



Besides the above- described external and internal glands, the 

 true nectaries of flowers are also of a glandular nature, and hold 

 a sort of intermediate position between them. They may be 

 termed, therefore, nectariferous glands. They are well seen at 

 the base of the coloured leaves of the flowers of the common 

 Buttercup {fig. 132) and Crown Imperial {fig. 133). These 

 glands consist of a depression into which a honey-like fluid or 

 nectar is secreted by the surrounding cells. The tissue of the 

 stigma of Flowering Plants is also covered by a viscid secre- 

 tion at certain periods, and may be considered therefore as of 

 a glandular nature. 



Fig. 132. 



Fig. 133. 



Fig. 134. 



Fig. 132. Petal of the Ranunculus with a nectary at 



its base Fig 1S3. Petal of Crown Imperial {Fri- 



tilJaria imperiaUs), with a nectariferous gland at 



its base. . Fig. 134. Lenticels on the branch of 



a species of Willow. 



On the young bark of most plants may be observed little 



brown, generally oval projections, which have been called 



lenticels, or lenticular glands from their supposed glandular 



nature {fig. 134). They have, however, no analogv with glands, 



E 3 



