MOUGEOTIA 8i 



not be cited as proof that the aplanospores so commonly found 

 among the Mougeotias are the result of lateral conjugation. 



Two unusual growth processes occur among several species of 

 Mougeotia, of which M. genuflexa and M. reinschii are the com- 

 monest examples; these are adhesion and genuflexion. It is true 

 that as new filaments appear in some permanent ponds, new 

 adhesions and genuflexions may continue to develop for several 

 successive months. Apparently cells coming in contact produce 

 growth substances which cause pectinization of the walls in con- 

 tact and increased growth of the wall at the point of contact. The 

 first results in adhesion; the second in genuflexion. 



Genuflexion is not an early stage in conjugation that has been 

 terminated before the development of tubes. There is no evidence 

 that it has either an advantage or a purpose, although various 

 authors have sought to find one. In one pond in which the process 

 occurred throughout the growing season during several successive 

 years, the interlocked filaments survived for a short time and then 

 fragmented and went to the bottom. No zygospores were ever 

 collected from this pond during the six years of observation. 



The steps in conjugation in the Mougeotias as in the other 

 genera in this family are probably activated in the same manner 

 as those observed by J. R. Raper in Achlya {Amer. Jour. Bot. 

 [1939-40]), a fungus in which the succession of hormones seems 

 to have been established clearly. 



Analogous changes occur in sexual reproduction though the 

 cells are not necessarily in contact. The first visible changes are 

 the growth of two papillae from nearby cells, until they meet, 

 adhere, and the walls in contact are dissolved. Possibly other 

 hormones lead to the movement of the protoplasts of both gam- 

 etangia into the conjugating tube, which meanwhile has greatly 

 enlarged, and growth has resulted in a form characteristic of the 

 species. Then follows the union of gametes and the deposition 

 of successive layers of the spore wall. 



With a few exceptions zygospores and aplanospores of Mou- 

 geotia have only two walls — an outer chitinous wall variously 

 colored and ornamented, and an inner transparent wall. In many 

 species the spores are enclosed by a sporangium wall, in others 

 the sporangium is merely a combination of gametangial and tube 

 walls. In some species the outer layer of the sporangium wall 

 changes to pectic compounds and forms a transparent layer 2 to 



