MARYLAND WEATHER SERVICE 173 



Typha zone. — There is some reason to believe that Typha lali- 

 folia follows Zizania on mud flats, but in many localities it must 

 be regarded as a pioneer. It is well adapted to fill this role on 

 account of the easy distribution of its seeds. Like Zizania it often 

 covers extensive areas. After Typha has occupied an area for a few 

 years it is apt to be invaded by Asclepias incarnata, Hibiscus 

 moscheutos, Polygonum arifolium, Polygonum sagittatum, Impa- 

 tiens biflora, Convolvulus sepium. In such situations Typha may 

 be partially replaced by groups of Scirpus lacustris, Scirpus validus, 

 Peltandra virginica, Orontium aquaticum and Iris versicolor. As 

 still drier conditions come to prevail, competition is more and more 

 severe and the following plants may enter into the struggle: 



Ceph alanthus occiden talis 

 Triadenum virginicum 

 Saururus cemuus 

 Aeschynomene virginica 

 Eupatorium perfoliatum 

 Epilobium coloratum 

 Cuscuta sp. 

 Ambrosia trifida 

 Micrampelis lobata 

 Helenium autumn a le. 



Alder zone. — Oephalanthus oceidentalis is often a pioneer shrub 

 in such situations, but usually the Alder (Alnus rugosa) follows 

 closely and becomes dominant. Many of the plants in the preceding 

 list persist in this zone, for the shade of the Alder is not dense. 

 Other shrubs generally accompany the Alder, e. g., Rosa Carolina , 

 Ilex verticillala. 



Maple zone. — On considerably drier ground beyond the Alder 

 flourishes the Red Maple, with which may be associated Black Wil- 

 low, Buttonwood and Ash. 



In any given locality several of these zones may be lacking, es- 

 pecially the first two. Very seldom is Pontederia absent, but the 

 conditions may not be favorable for Zizania (vide Scofield, 1. c). 

 Typha is not so exacting in its requirements, and is universally pres- 



