28 A FIELD GUIDE IN NATURE-STUDY 



What is the position of the cluster in which the fruits are yet unripe? 

 Examine one of the fruits with its silky parachute. What position does 

 it take when sailing in the air ? Take hold of the parachute and gently 

 pull what appears as the seed between thumb and finger. Do you feel the 

 tiny points on it ? Move it in the opposite direction. Do the projections 

 have their points turned up or down ? Of what use are these hooks to a 

 ballooning seed ? 



Weed travelers. 'List on the opposite page fifty of the weeds you know 

 and indicate in each case of what part of the world the weed is a native. 

 The information can be found in Gray's Manual or similar botanical texts. 

 Unless it is stated that the plant was introduced from some foreign locality 

 the presumption is that it is native to North America. Would you call 

 weeds good travelers? Find the facts regarding the date of introduction 

 of the Russian thistle to this country and the rate of its spread; of Jimson 

 weed; of deadly nightshade. 



Definition. A weed might be defined as an eminently successful plant 

 growing where man does not want it. It is because they are such bold, 

 adventurous, capable organisms that they are interesting. Let us inquire 

 why weeds are so successful that they perpetually threaten man's attempt 

 to cultivate his corps. 



Rate of seed production. Most of them produce enormous quantities 

 of seeds. Count the number of seeds in a pod of the wild mustard, bouncing 

 Bet, or any other annual. Count also the number of pods on one good- 

 sized plant. How many seeds does this plant bear ? On the basis of this 

 average calculate how many years it would take to cover the land's sur- 

 face, starting this year with a single plant and supposing that all seeds find 

 a place to grow and none die. Can you find out from any source how many 

 seeds single plants of the following weeds produce: white mustard, tall 

 pink root, lamb's-quarters, purslane ? Lift out a square foot of soil two 

 inches deep from some spot in a vacant lot and put it in a shallow box. 

 Keep it moist, in the schoolroom, and count the number of weeds that 

 appear. In the same way take up the next four inches of soil and record 

 the number of weeds that grow from it. It will be interesting to find out 

 to what depth there are weed seeds that will germinate. There are stories 

 printed occasionally in the newspapers that seeds buried along with mum- 

 mies in the old Egyptian days have germinated when planted. Find out 

 what experiments have shown to be the maximum length of life of seeds 

 and record the result here. 



Methods of dispersal. Seeds have facilities for wide dispersal. Why 

 is it essential that seeds should be carried away from the parent plant? 

 List here some of those that are carried by wind and draw three such. 



