28 THE MICROSCOPE. 



specimen be macerated in water for a few days ; this 

 will remove the gum. If the portion of wood you 

 wish to study be dry, you must moisten it in water for 

 some time to soften it, then treat it as you would 

 green wood. It may be necessary in some cases to 

 use boiling water to render the stems sufficiently soft 

 for making sections. Wet the surface of the wood, 

 and cut off as thin a transverse section as possible. 

 Instruments called " section instruments " are sold for 

 this purpose, and very handy and useful some of them 

 are ; you can add one to your microscopic apparatus 

 after you have had more experience ; but you will 

 find that, with care and perseverance, you will succeed 

 in making very thin sections of stems, which will show 

 their different parts, such as the pith, medullary rays, 

 bundles of wood and bark, quite satisfactorily. In 

 the examination of the reproductive organs of plants, 

 you will find exhaustless matter for study and contem- 

 plation. Every one is familiar with the dusty particles 

 contained within the stamens of different plants, called 

 pollen (Fig. 8). Various and very 

 beautiful are these pollen forms, and 

 easy enough to examine, so far as 

 the external appearance goes. Per- 

 haps their most common form is 

 spherical or elliptical ; but many 

 beautiful geometrical forms are met 

 L with, such as cubic, tetrahedral, poly- 

 gonal, &c. In structure, the pollen grain generally 

 consists of an internal cell membrane, with one 

 or more outer layers of firmer texture. In some 

 instances, as in the Zostera marina, there is 

 only an inner membrane. The outer covering may 

 be smooth, or rough with numerous spiny pro- 

 jections, or reticulated, or divided into several seg- 

 ments or bands, or beset with numerous pores 



