60 THK GENERAL DEVELOPMENT OF PLANTS. 



may be readily found in the stalks of the Rhubarb, the Four-o'clock, 

 the Arum or Indian Turnip, and the Calla. In the latter plants, a 

 crystal-bearing cell in the leaf may often be detached entire from 

 the surrounding tissue : when moistened, it absorbs water by endos- 

 mosis, becomes distended, and may sometimes be seen to eject its 

 crystals one by one, in a curious manner, through a minute perfora- 

 tion at one or both ends (Fig. 73). As to their composition, these 

 crystals more commonly consist of oxalate of lime ; but those of car- 

 bonate, sulphate, or phosphate of lime are not unfrequent. 



95. Cystolithes are a peculiar structure composed of crystalline 

 mineral and of vegetable matter combined, of common occurrence in 

 the leaves of the Fig, Hop, Mulberry, and all the Nettle family, 

 just beneath the epidermis. They are globular or club-shaped 

 bodies, or of various other forms, usually hanging by a short stalk 

 in an enlarged cell: their principal mass is found to be cellulose; 

 but then- surface is studded with crystalline points of carbonate of 

 lime. 



CHAPTER II. 



OF THE GENERAL DEVELOPMENT AND MORPHOLOGY OF PLANTS. 



96. Having ascertained what vegetable fabric consists of, we are 

 prepared to consider how these organic materials, the cells, are com- 

 bined to constitute a vegetable, what the parts or organs of plants 

 are, how they are related to each other, and how they live, grow, 

 and perform the work of vegetation. Viewing plants as individual 

 beings, we may now proceed to study their Organography or Mor- 

 phology (3). 



97. Plants occur under the greatest diversity of forms. Some 

 kinds are of the utmost simplicity ; and many of these are so minute, 

 that separately they are invisible to the naked eye, and become 

 apparent only by their aggregation in vast numbers. Others are 

 highly complex in structure, and may attain a great size, such as 

 gigantic trees, some of which have flourished for a thousand years 

 or more. But each plant or tree, however vast or complex it may 

 become, commenced its existence as a single vegetable cell, by the 



