CLEISTOGAMY IN HETERANTHERA 

 DUBIA 



By Robert B. Wylie 



The submersed aquatic plants offer an interesting field for 

 study because of tbeir double adaptations. As land plants they 

 developed complex vegetative bodies and achieved the flower and 

 seed habit. Then as water plants they faced the problem of 

 adjusting that body and their methods of reproduction to rad- 

 ically different conditions from those under which their dominant 

 traits were evolved. Among these plants are found varying de- 

 grees of specialization, and doubtless many are in process of 

 transition to the new habitat. 



The more highly specialized have elaborate structures and 

 methods for accomplishing cross pollination at the surface of the 

 water or while still submerged at a considerable depth. Among 

 the members of these groups there is a pronounced tendency 

 towards dicliny and most of them are dioecious. On the other 

 hand, the production of perfect flowers in combination with a 

 submerged vegetative body is commonly associated with the habit 

 of raising an inflorescence completely above the surface of the 

 water. In these the method of pollination is still essentially that 

 of the land plant often without special modification. These two 

 tendencies lessen the probability of close pollination in w^ater 

 plants and doubtless account for the infrequent reports of cleis- 

 togamy among the submersed aquatics. 



Plants having submersed vegetative parts in association with 

 unspecialized inflorescences and perfect flowers have difficulties 

 in cross pollination. Heteranthera du'bia (Jacq.) MacM. belongs 

 to this group and is without special adaptation to air, surface, 

 or subsurface pollination. 



In connection with work at the Macbride Lakeside Laboratory 

 on West Okoboji lake in northwestern Iowa there was favorable 

 opportunity for the study of this species which grows abundant- 



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