36 



INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



2. Butomus type. In this case the formation of the periplasmo- 

 dium occurs a little earlier, when the microspores are still grouped 

 in tetrads. Examples: Butomus, Stratiotes, and Ouvirandra. 



3. Sparganium type. Here also the fusion of protoplasts begins 

 at the tetrad stage but the tapetal cells are multinucleate. Ex- 

 amples: Sparganium, Typha, Tradescantia. 



4. Triglochin type. In a few plants the tapetum begins its activ- 

 ity while the microspore mother cells are still undergoing the meio- 

 tic divisions. The tapetal protoplasts and nuclei protrude into the 



\.:-v..i. 



Fig. 29. Tapetal Plasmodium in Symphoricarpos racemosm (A) and Lonicera 

 pyrenaica (B). (After Moissl, 1941.) 



spaces between the mother cells so that the periplasmodium is 

 formed at a very early stage. Examples: Triglochin, Potamogeton, 

 and several members of the Araceae. 



Like the glandular or secretory tapetum, the amoeboid tapetum 

 also serves for the nutrition of the spores, and is probably more 

 effective for this purpose. As some authors (see Mezzetti-Bamba- 

 cioni, 1941) have suggested, it seems probable that the periplas- 

 modium contributes to the formation of the exine, but this point 

 deserves further study. A curious feature which has been observed 

 in several plants (see Ubisch, 1927; Kosmath, 1927; Kajale, 1940; 

 Puri, 1941; Singh, 1950) is the appearance of small granular mark- 



