18 



FUNDAMENTALS OF CYTOLOGY 



~the second fewer and larger coenocytic compartments, while the third is 

 completely coenocytic, having no cellular subdivisions whatever in the 

 vegetative body. Their common body form must be developed by what 

 is common to all of them — nucleated c^^toplasm. 



Even more striking are the spore-bearing organs of various plants 

 (Fig. 10). In each of these selected cases the organ is composed of a 

 supporting stalk and an enlarged terminal portion in w^hich the spores are 

 formed. In the first, a fruiting body of a slime mold, a multinucleate 

 Plasmodium grows upward into a column which enlarges at the top, 

 becomes surrounded by a resistant outer wall, and develops an internal 

 system of capillitium filaments, and then, only when these differentiations 

 are practically completed, does the multinucleate protoplasm in the up- 

 per portion subdivide into spores. In the second, a fruiting body of 





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Fig. 10. — Differentiation in spore-bearing portions of various plants. Semidiargainmatic. 

 Explanation in text. (A'o. 4 redrawn from J . L. Williams.) 



another type of slime mold, a large number of separate cells become closely 

 aggregated without actually fusing and build up a stalked structure wdth a 

 slimy sheath and spore-like cysts. In the third, a sporophj^te of a liver- 

 wort, a mass of multicellular tissue develops the stalked form, a sporan- 

 gium wall, a system of internal filaments (elaters), and eventually spores. 

 In the fourth, a sporangium of an alga, a single uninucleate cell elongates, 

 projects from the body, and forms a distal globular enlargement which 

 subdivides into spores. In the fifth example, the fruiting body of a 

 mushroom, the organ is developed by a mass of interwoven filamentous 

 hyphae. 



Of equal interest in connection with the role of cells in structural and 

 functional differentiation are the following observations on the develop- 

 ment of animal eggs. The larva of a certain annelid w^orm develops 

 much of its characteristic form and internal differentiation up to a certain 

 stage even when the normal subdivision into cells is suppressed by adding 

 KCl to the medium. In some marine animals a complete embryo may be 

 developed by a single one of the 8 or 16 cells formed by the first 3 or 4 

 divisions of the fertilized egg, whereas in others the embryo lacks certain 



