87 ELEMENTAL Y 77.s.sr/-;>. 



thoroughly with water and add strong sulphuric acid. After a few 

 minutes repeat the operation of washing. 



The acid renders the cellulose cell-wall transparent, and the 

 protoplasmic strands can be seen connecting the masses of contigu- 

 ous cells. If this does not show clearly stain the preparation with 

 aniline blue. The sections can be permanently mounted in a drop 

 of glycerin jelly. 



Strasburger, p. 371 ; Quart. Journ. Micros. Science, 1882, p, 

 365, 1883, p. 151; Bot. Gazette, 1881), p. 83. 



II. Collenchyma Tissue. 



This tissue is composed of parenchyma like cells with walls 

 thickened at the corners, or points of contact, and usually f"j>< ////</ 

 at the ends. They form cylinders of tissue beneath the epidermis 

 in many herbaceous stems and petioles. The cells often contain 

 chlorophyll and are sometimes capable of division. 



Illustration: COLLENCHYMA CELLS from a mature stem of the 

 BEGONIA, or GERANIUM. 



PREPARATION FIRST: Transections of a stem 3 to 4 m.m. in 

 diameter should be cut free hand, stained with haematoxylin, and 

 mounted in glycerin jelly ; or better, hardened in alcohol, infiltrated 

 with collodion, sectioned, and mounted as duected on p. 21. 



OBSERVE: 1. Thin walled cells forming the epidermal tissue 

 of the stem. 



2. Inside of this a ring of f/lf#h /////// thick walled cells form 

 ing a zone about the stem. 



3. The latter, the collenchyma tissueis composed of cells with 

 walls comparatively thin along the lateral surfaces, but thickened 

 at the angles. This tissue is very strong and contributes greatly 

 to the strength of the stem. 



Make a longitudinal section of the stem and examine the cells 

 of this zone. 



De Bary, p. 119; Strasburger, p. 106; Goodale, p. 65. 



Endodermal Cells. 



A modified form of thick walled parenchyma is found in the 

 ENDODERMIS, in most roots a single layer of cells, surrounding the 

 fibro-vascular bundles of the central cylinder. (Figs. 17, 22.) 



