HARSHBERGER : PHYTO-GEOGRAPHIC SKETCH 135 
L., Philotria Canadensis (Michx.) Britton, Acorus Calamus L., 
Iris versicolor L., Myriophyllum verticillatum L., § pirodela polyrhiza 
(L.) Schleid., Cardamine bulbosa (Schreb.) B. S. P. (C. rhombotdea 
DC.), C. rotundifolia Michx., Caltha palustris L., Myosotis palustris 
(L.) Lam., Roripa palustris (L). Bess. (Nasturtium palustre DC.), 
Koripa Nasturtium (L.) Rusby (Nasturtium officinale R. Br.) (Vas- 
turtium association), /suardia palustris L. (Ludwigia palustris 
Ell.) and various algae, viz., Spirogyra, Hydrodictyon, Conferva, 
Nitella, Oedogonium, Volvox, Luglena and Mesocarpus. 
TIDAL-MARSH-PLANT FORMATION. — This formation was studied 
along the Delaware and at the mouths of the Schuylkill river, 
Crum and Darby creeks. The most satisfactory place to study 
the ecologic disposition of the plants is at the mouth of Crum 
creek, where the botanist can take advantage of a wooden foot- 
bridge (two thousand feet long) constructed to connect a light- 
house with the mainland (Fic. 1). The tidal marshes have been 
formed by a variety of contributing forces. Material brought 
down by the rivers has been sorted and distributed over the tidal 
areas by the tides and currents of the streams that meet here. 
The location of these deposits and their superficial extent has de- 
pended upon the character, force and direction of the currents. 
Elaborate plans are in existence showing the currents of all the 
Navigable streams in southeastern Pennsylvania. These may be 
consulted at the office of the United States engineer in charge of 
harbor improvements. The material is too abundant and the 
details too specialized to present in a paper of this character. 
The banks of the streams influenced by tidal action are lined 
by thickets composed of Platanus occidentalis L., Gleditsia tria- 
canthos L., Alnus rugosa (Du Roi) K. Koch, (Adnus serrulata 
Willd.), Acer ruérum L., Salix alba L., Liquidambar Styracifiua L., 
Fraxinus Americana L., Sambucus Canadensis L., Cephalanthus 
occidentalis L., Rosa lucida Ehrh. with Parthenocissus quinguefolia 
(L.) Planch. (Ampelopsis quinquefolia Michx.) and Rubus nigrobac- 
cus Bailey. The herbaceous associations of the woody plants men- 
tioned are in this rich alluvial soil Thalictrum polygamum Muhl., 
Fleracleum lanatum Michx., Agrimonia parvifiora Soland., Allium 
vneale L., Ambrosia trifida L., Impatiens biflora Walt. (/. fulva 
Nutt), In mud near the bank, associations of the rose mallow, 
