THE LEAF. 243 



tact. They are cellular, and found in the substance 

 of the epidermis, at the base of hairs, as in stings, or 

 carried on the summit of hairs, as in Fig. 413. 



Such hairs give to plants an appearance as if 

 covered with little pellucid dew-drops. Look at the 

 hairs of all sorts of plants through the microscope. 

 You will find that glandular hairs are by no means 

 uncommon. 



Fig. 412 (b) represents a sting. It consists of a sin- 

 gle cell, fixed upon a gland, filled with irritating juices. 

 When the hair is disturbed, the liquid of the gland 

 passes through it, and is injected into the disturbing 

 object. Glands are sometimes buried in the bark, 

 but they are always near the epidermis. Cavities 

 containing gums, resins, etc., are analogous to glands, 

 but buried more deeply in the substance of the plant. 



Bracts, sepals, and petals, are constructed in the 

 same way as foliage-leaves. Their framework is fibro- 

 vascular, and filled in with parenchyma, which con- 

 tains various coloring-matters instead of chlorophyll ; 

 and over all there is spread a delicate epidermis, more 

 or less studded with stomata. The sepals of mono- 

 cotyledons are parallel-veined, and those of dicotyle- 

 dons are net-veined. When petals have long claws, 

 the fibro-vascular bundles traverse them, and sepa- 

 rate, to form the framework of the limb, which is 

 composed of spiral vessels and elongated cells. 



If you examine the structure of the filament, you 

 will find it composed of a central bundle of spiral 

 vessels and delicate woody tissue, which terminate in 

 the connective. They are surrounded by a layer of 

 cells, covered by the epidermis. The anthers are en- 

 tirely cellular, the pollen cavities being lined with a 



