93 ELEMENT A It Y T1S8 UES. 



than the sectioned pits and are the cells of the Medullary Rays-in 

 cross-section. 



OBSERVE in (2): 1. The form of the Tracheids in cross-section. 



2. The " middle-lamella " in the cell-wall of each. 



3. The Bordered-pits and Medullary Mays in the section. 



4. The Resin-passages in section. These are large openings 

 surrounded by irregular thin-walled cells containing resin. These 

 passages often occur running transversely, following^the larger 

 medullary rays. (Fig. 14.) 



5. The annual layers of tissue (seen best with a low power) 

 marked by alternating layers of larger and smaller cells, and 

 crossed at right angles by the Medullary rays. (Strasburger pp. 

 115, 128a.) 



6. The entire absence of true Tracheae, these being found in 

 Gynmosperins only next the pith. In structure Tracheids seem to 

 be intermediate between Fibrous tissue and Tracheae. Bessey, pp. 

 25, 26 ; Goodale, p. 83 ; DeBary, pp. 159, 160 ; Vines' Text Book of 

 Bot., p. 200 ; Strasburger, p. 56. 



V. (d) Tracheae. 



Illustration: Sections of steins for the study of TRACHEAE, 

 VESSELS or DUCTS. The following general forms will be examined: 



(a) Dotted. (c) Spiral. (e) ticalariform. 



(b) Pitted. (d) Reticulated. _(f) Annular. 



For these studies the woody tissue is to be treated as directed 

 for the previous illustration, but in the case of herbaceous stems 

 the tissue should be hardened in alcohol and carried through' the 

 method for mounting, outlined on p. 21. 



PREPARATION FIRST: (a) Longisectioii of GRAPE VINE STEM. 



OBSERVE: 1. In the region of the section containing the tibro- 

 vascular tissue, the large well developed ducts with pitted surfac.es. 



2. These dots are true openings allowing free communication 

 between contiguous cells. Goodale, p. 29 ; Bastin, p. 162. 



PREPARATION SECOND: (b) Radial longitudinal section of the 

 stem of CASTOR OIL BEAN, 1 c.m. in diameter (thin section mounted 

 in water). 



OBSERVE: 1. Rectangular cells of pith and cortex. 



2. In the vascular region ; large thick walled ducts, with the 

 surface covered with bordered pits. 



