158 The Mode of Examining ilie \TmullJuJ.^!t^l 



epidermis. The formation of the cork layer can be well seen in 

 young shoots of the Black Currant. The epidermis is a unicellular 

 layer ; but in a few plants, as the Begonia, we have two, the second 

 being formed by the division of the first into two. In the cells of 

 the epidermis we do not find intercellular spaces, the stomata fur- 

 mshing the means of communication with the subjacent tissues, 

 Stomata may be absent, as in roots and submerged parts of plants. 

 The external cell-wall of the epidermis is in general greatly thick- 

 ened, forming what is called the cuticle. The cuticle is a continuous 

 layer, often very largely developed and affording a considerable 

 amount of protection to the more delicate tissues below. The 

 various epidermal appendages must also be examined along with the 

 hmitary tissues. Hairs are developed by the epidermal cells, the 

 hair appearing as a projection of one part of the cell. Hairs are 

 variable in form. Boot hairs are to be found in Marchantia, Equi- 

 setum, &c. ; woolly hairs, either temporary, as in the bud of the 

 Horse-chestnut, or permanent, as in certain species of Stachys, &c. 

 Jointed or beaded hairs in Tradescantia, the branching hairs of Ver- 

 bascum, Tm-nip, &c., stinging hairs, as in Nettle, Loasa, &c., which 

 generally contain silica, are famihar objects. Glandular hairs, as 

 in Rose, and scales, as in Sea-buckthorn, &c., are also to be consi- 

 dered as part of the limitary tissues. Stinging hairs are generally 

 placed on an elevated portion of the epidermis. The scales of ferns 

 seem to be modified hairs, the contents of the cells rapidly disappearing, 

 and the hair becoming dry and chaff-like. The prickles of the rose 

 are modified hairs, and seem to be developed by the glandular hairs. 

 The stomata of plants form an endless variety of objects for the 

 microscope. In general, they are developed from single epidermal 

 cells. In the Marchantia several cells enter into their construction, 

 while in a fern, Anemia, the stoma is developed in the centre of an 

 epidermal cell. Besides the collenchyma, cork must also be con- 

 sidered as one of the limitary tissues. Cork forms a protecting 

 covering, and also is of great importance in the healing of wounds in 

 plants. The cork ceUs are developed from the so-called cork cambium. 

 In large plants and trees we find three stages of the Hmitary tissues, 

 each of which requires to be studied. On the youngest twigs we 

 have a true epidermiis ; farther down we have the corky layer, the 

 periderm, formed; while still farther from the growing point we 

 have the bark. The last point that calls for mention in regard to 

 the Hmitary tissues is the peculiar corky deposits called Lenticels. 

 They are common on Willows, and have been described as glands. 

 They, however, seem to be little masses of cork ceHs, and do not 

 possess any secreting structure. 



Fibro-vascular hundles. — In the tissues of all plants with true 

 roots we find string-Hke masses of tissue permeating in every direc- 

 tion, and forming a more or less complete skeleton. These are the 



