164 HOW TO WORK 



Almost all vegetable tissues are most easily investigated when 

 they have been preserved for some time in viscid media, which are 

 miscible in all proportions with water. , Leaves and stems when 

 well saturated with syrup or glycerine are easily dissected into their 

 component tissues. They must first be placed in very dilute 

 solutions, which may be concentrated by very gradual evaporation, 

 or the strength of the solution may be increased by the addition of 

 small quantities of strong syrup or glycerine from day to day. The 

 beautiful textures to be demonstrated in jams and preserved fruits 

 have been alluded to in p. 73. 



Very hard vegetable textures, such as the shell of the cocoanut, 

 walnut, &c., may be cut into thin sections, according to the plan 

 described in p. 83. 



Pollen grains are among the most interesting objects. They are 

 easily procured by shaking the anther of any flower fully expanded 

 upon a glass slide, and may be mounted dry, p. 75, in aqueous fluids, 

 p. 75, or in Canada balsam, p. 76. 



77/6' external markings of the seeds of plants are well worthy of 

 attentive examination. The student may examine the seeds without 

 any preparation whatever, as dry objects, p. 75, by reflected light. 

 Many seeds may be at once recognised, and the species of plant 

 to which they belong, determined by the markings on the testa 

 alone. 



The starch globules enclosed in the cells of many seeds and some 

 rhizomes exhibit great variety in form, size, and structure. Different 

 kinds of starch should be submitted to examination, and every 

 student should be familiar with the microscopical characters of wheat, 

 rice, and potato starch, pi. XXXVIII, figs. 239, 240, 241, arrowroot, 

 and Indian corn. 



The colouring matters of leaves and flowers are contained in cells, 

 and are formed by the germinal matter of each cell. Rven in petals 

 of different plants, of precisely the same colour, different kinds of 

 colouring matter have been recently detected by Mr. .Sorby. See 

 "Spectrum Microscopic Analysis," in part III. The petals of many 

 flowers may be preserved without difficulty, as they retain their 

 characters when dried. They should, however, be covered with 

 thin glass to protect them from the dust. 



If the student desires to study the manner in which the colour- 

 ing matter is formed within the cell, he must examine recent speci- 

 mens in glycerine, according to the principles laid down in part V. 



The crystals or raphides found in many plants are well wprthy of 

 attentive study. They differ in composition and form in different 

 plants, and it is even possible to recognise some species by the 



