174 ECOLOGY 



B. Test some of the following water-carried fruits and seeds 

 to see which will float longest : aquatic grasses, rushes, and 

 sedges, polygonums, water dock, bur reed, arrowhead, water 

 plantain, pickerel weed, alder, buttonbush, water parsnip 

 (Sium), water hemlock (Cicuta), water pennywort (-Hj/tiro- 

 cotyle), lotus (Nelumho). 



C. Sketch and describe in detail the fruit or seed which 

 appears to be best adapted to each of the four modes of dis- 

 persal above mentioned (Sec. 152, D). 



COMPETITION AND INVASION 



154. Field study of competition. 



A. Find a spot in wliich many weed seedlings iiave sprung up, stake off 

 one or two square feet, count the plants, and tiien watcli their growth 

 for as long a period as possible. Stake off a similar plot, pull up all 

 but one or two of the weeds, and compare the growth of these plants 

 with that of the crowded ones. 



B. Beginning as soon as weed seedlings start in the spring, stake off a 

 square foot of very weedy ground, pull up and count all the seedlings 

 which grow on the plot, continue the count as others spring up, and 

 make a list of the kinds obtained i and the total number of each kind. 



C. Allow any large, vigorous weeds to grow up among lettuce, radish, 

 carrot, or other seedlings, and notice which set of plants prevails. 

 Give as many reasons as possible for this result. 



References. Clements, 59 ; Principles, Chapter XXXIV. 



155. Field study of invasion.* * 



A. Look for places in which pastures or mowing fields are beginning to 

 " run out," and daisies (Chrysanthemum), sorrel (Rumex), cone flowers, 

 and similar weeds are taking the place of the grass. 



Look for a lawn that iS too much shaded and becoming filled with 

 chickweed or other weeds. 



B. Find a pond in process of drying up and notice what changes are 

 taking place in the character of the vegetation. 



C. Study an abandoned strawberry bed. 



D. Examine a clearing in which young saplings have begun to grow to a 

 height of 15 or 20 feet. In every case make a list of the older inhabit- 

 ants of the territory i and of the newcomers i and give as many reasons 



1 Identified by the instructor. 



