8fi ELK MK. \TAIiY TlXS 



iodide of zinc, and observe that the cell walls are colored yellow or 

 In-oirn the character istic test for Ijiyniti.. What would be the 

 reaction with pure cellulose? Zimmermann's Microtechique, p. 

 143; Goodale, p. 36; Vines' Text Book of Bot., p. 107 ; Strasbur- 

 ger, pj>. 59, 119. 



Illustration Third : Cell walls containing CUTIN. Epidermis 

 of most plants, and in many tissues where cell walls are to be 

 strengthened, or protection secured. 



Make thin transections of the leaf of Pinus Sylvestris or 

 Cycas, and mount in water. 



OBSERVE: 1. The small epidermal cells with outer walls 

 much thickened, usually in layers by the formation of cutin. The 

 cutin can be removed by leaving the tissue in strong chromic <i<-'nl 

 for some time. After this, wash the section with water and add 

 chlor-iodide of zinc. Note the blue color, the reaction for cellulose, 

 forming the greater per cent, of the inner part of the wall, 

 while the outer part consists of nearly pure cutin. Vines' Text 

 Book of Bot., p. 107 ; Goodale, p. 38 : Strasburger, p. 58 ; DeBary, 

 p. 78. 



Illustration Fourth: Cell walls containing MINERALS, in 

 CRYSTALLINE or AMORPHOUS forms. (Stems of Cereals, and many 

 Sedges.) The substance most frequently present is Silica. To 

 test this, ignite the specimen in a platinum dish, treat with nitric 

 acid, and again ignite. The silica remains behind, and often 

 retains the microscopic form of the tissues. This is true with the 

 stems of Equisetum (horsetails.) 



Crystals of Calcium salts can be found in the cell walls of the 

 bast tissues of the willow and many GynmosperniK. For further 

 study of the subject, examine Vines' Text Book of Bot., p. 108 ; 

 Goodale, p. 39 : DeBary, p. 102. 



Continuity of Protoplasm. 



Illustration: Stem of Aesculus (common horse-chestnut.) 

 PREPARATION: By the use of a knife remove the outer dark 

 colored and inner gree;n bark (periderm), from a young growing 

 stem, about 1 c.m. in diameter. With a sharp razor make thin 

 tangential sections of the exposed whitisli tissue (cortex), and place 

 in a solution of iodine in potassic iodide until brown. 



