MORPHOLOGY 



11 



constricted (Fig. 2). Cylindrical and also disc - shaped forms are 

 common to various Algae. The Diatomeae (Fig. 3), in particular, 



furnish a great variety 



of spindle, canoe, helmet, 



and fan-like shapes ; but 



they may all be derived 



from the more simple Fl °- ^-saxHummyces 



1 1 -.. -it cerevisiae. 1, Cells 



spherical, discoidal, or without buds ; 2 and 

 cylindrical forms. The 3, budding ceils, (x 

 Bacteria, which, as the M0,) 

 cause of contagious diseases and of de- 

 composition, have been the object of so 



a, Commencement of division; much recent investigation, also exhibit a 



b, shortly after division; c, a great diversity of form. A small quantity 



later stage. (xMO.) of ^ white deposit on ^^ ^ ^^ 



examples of spherical, rod-like, fibrous, and spiral bacteria (Fig. 4). 

 In the course of the development of a single species several of 



Fig. 1. — Gloeocapsa polydermatica. 



Fig. 3. — Pinnularia viridis. jf, Surface 

 view ; B, lateral view. (x540.) 



Fig. 4. — Bacteria from deposits on teeth, a, 

 Lcptothrix buccalis; a*, the same after treat- 

 ment with iodine ; b, Micrococcus ; c, Spir- 

 illum dentium after treatment with iodine ; 

 d, comma bacilli of the mucous membrane of 

 the mouth. (x800.) 



these different forms frequently occur. The next stage in the pro- 

 gressive development of external form in the vegetable kingdom 

 is exhibited by such plants as show a differentiation into apex 



