138 HARSHBERGER : PHYTO-GEOGRAPHIC SKETCH 
until the island becomes dry enough to support tree vegetation. 
The disposition of the several associations of plants can be studied 
best by reference to the graphic representations of plant distribution 
accompanying the text. The marshes have been drained in many 
cases sufficiently to raise marsh-grass for hay. The ditches of 
such converted marshes afford many interesting plants, such as 
Fic. 2. Porti f tidal-marsh-plant f tion shown in Fig. 1. A, area of Zizania 
ase L.; £, Nuphar seacelation ify Sagittaria latifolia Willd. and Ambrosia trt- 
jida L KK, Sambucus Canadensis L., Cephalanthus occidentalis L. and Rubus nigro- 
Hise er. KEKE, area occupied = willows, W, and Sambucus Canade nsis L. 3 
Hf, Hibise. sie Miehanres Ls O, /mpatiens biflora Walt., Rudbechia latifolia Willd. and 
Sagittaria latifolia Willd. ; M, Thalictrum polygamum Muhl. and Heracleum lana- 
tum Michx. 
Spirodela polyrhiza (L.) Schleid., Lemna minor L., Wolffia Brast- 
zensis Wedd., W. Columbiana hak (Lemna association), Ponte- 
devia cinate L. (Fic. 4, C), Asclepias incarnata L., Typha latifolia 
L., Sagittaria subulata (L.) Buchenau (S. pusilla Nutt.), S. rigida 
Pursh (S. heterophvila Pursh), S. latifolia Willd., Zizania aquatica 
