244 PRACTICAL BOTANY 



shape to the cells of the rays : it is thin-walled, with 

 granular protoplasm and nucleus. (Compare Fig. 9, C, 

 p. 107.) 



If these sections be treated with dilute potash, and 

 mounted in glycerine, their structure may be more 

 easily made out. 



C. In sections passing through the phloem will be 

 seen 



i. The medullary rays as before, but their form is 

 more convex : all the tissues between the medullary 

 rays' are derived from cambium-cells of the form above 

 observed. These are 



ii. Sieve-tubes, which retain the form of the cam- 

 bium-cells : the cellulose walls seen in surface view are 

 smooth : those cut longitudinally appear of wavy out- 

 line (sieves) : the structure of the latter is well seen 

 after treatment with chlor-zinc-iodine for twenty-four 

 hours. The contents consist chiefly of transparen 

 protoplasm. 



iii. Bast-parenchyma, derived from cambium-cells 

 by their division by transverse walls. 



iv. Some few cells, especially towards the periphery 

 containing crystals which give v the reactions of calcium 

 oxalate. 



THE LEAF. 



Examine the bifoliar spur of Pinus sylvcstris as a 

 whole : it consists of a very short axis, at the base of 

 which are borne membranous sheathing scales, and at 

 the apex two long needle-shaped folia^ j ] c in other 

 species of Pinus the number may be lar^r. Note that 



