US OF THE MICROSCOPE IN BOTANY. 35 



a transverse section of any seed, you will find it has 

 two coats, an outer and inner membrane called re- 

 spectively testa and tegmen; you will see the embryo 

 either surrounded by albumen or immediately invested 

 by the coats. The following easily procured plants 

 will furnish you with samples of seed-forms : poppy, 

 stitchwort, mignonette, snapdragon, saxifrage, sweet- 

 william, foxglove. You can add to this list almost 

 indefinitely. 



Every stream, ditch, and pond will supply. you ; 

 with many forms of algae, known as Diatomacecz and 

 Desmidiacetz* Once these organisms were supposed to 

 belong to the animal kingdom, on account of some 

 ot them exhibiting motion ; there is no doubt, how- 

 ever, that both these families are true vegetables'. 

 They are found in masses of jelly-like substance 

 attached to the stems or leaves of various aquatic or 

 marine plants, or they envelop any submerged plant 

 with loose brownish flocculent matter. The Diatomacece, 

 or brittleworts, are invested with a covering of silex ; 

 this fact you can readily demonstrate for yourself by 

 boiling the minute plants in nitric acid, having pre- 

 viously washed them well, so as to free them from 

 extraneous matters. The organic vegetable matter 

 is destroyed ; the siliceous portion remains. The 

 Desmidiacece, another family of confervoid algae, are 

 destitute of any siliceous covering ; they are generally 

 of a green colour, and are found, like the Diatomacece, 

 investing submerged plants or other bodies. These 

 microscopic algae, under a power of 300 to 400 

 diameters, are very striking objects; they come "in 

 such questionable shapes " that you cannot help but 

 " speak to them." Now circular, now filamentary, 

 beautifully jointed, now like small boats in outline, 

 now crescent-shaped in fact, every variety of form 

 exhibiting these algae, I have no doubt, will occupy 



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