174 



PART Ii. VEGETABLE HISTOLOGY. 



latex and prevent its escape from the vessels. Sections should then be made 

 longitudinally through the bark. The long, somewhat branching cells may be 

 traced by means of their granular, dark-colored contents, the coagulated latex. 

 The vessels may usually be more satisfactorily traced by dipping the section for 

 a few moments in nitric acid, rinsing well in water and then staining in an 

 aqueous solution of methyl-green. 



Complex laticiferous tissue may be studied by making similar longitudinal 

 sections of Dandelion or Chicory Roots. Similar precautions should be observed 

 to prevent the escape of the latex from the vessels. Study, also, the distribu- 

 tion of the tissue as it appears in a cross-section of the root. 



Make drawings of both kinds of laticiferous tissues. 



Make transverse and longitudinal sections of the stems or petioles of the 

 Bulrush, Yellow Water-lily or Pickerel weed, and make studies and drawings 

 of the large intercellular air-spaces. Note, also, the trichoblasts, found abund- 

 antly in the Yellow Water-lily. 



For the study of secretion reservoirs, sections of the rhizome of Alalia 

 nudicaulis of the root of Aralia racemosa, of the stem of any Umbelliferous plant, 

 or of the twigs of Pines or Firs, may be made. They may easily be recognized 

 from the descriptions already given. 



CHAPTER III. 



-TISSUE SYSTEMS. 

 PLANTS. 



ORGANS OF 



The tissues of plants are not scattered without order through 

 the vegetable structure, but are grouped into systems. Usually 

 three tissue-systems are recognized, the epidermal, the fibro- 

 vascidar, and the fundamental. 



i. — The Epidermal System. This includes the epidermis 

 and its various appendages, stomata, water-pores, hairs and 

 glands already described. Its function is chiefly protective, 

 and particularly to protect the plant against the excessive evap- 

 oration of water from its interior tissues. To this function the 

 compact arrangement of the cells and the cutinization of their 

 walls admirably adapt them. 



2. — The Fibro- Vascular System. This constitutes the 

 fibrous frame-work of the plant. In the leaf, it is the system of 

 veins, and in the stem and root the tough and resistant portion. 

 Its function is partly to give strength to the organs of which it 

 forms a constituent part, and partly to conduct the fluids of the 

 plant from one part to another. 



