WEEDS OF CITIES AND TOWNS. 17 



ware, sweepings from elevators and grain stores and refuse from 

 kitchens. In many instances the lots are low and the owners have 

 them filled with the material mentioned, thus furnishing an excel- 

 lent seed bed already planted for many a weed. Oftentimes these 

 weed patchs are wholly or partly surrounded by high bill-boards, 

 thus hiding the weeds from sight and allowing them to flourish 

 without molestation. 



These city and town weeds, as long as growing vigorously, are 

 somewhat beneficial in that they serve to purify the air by using 

 carbonic acid gas and throwing off oxygen. As soon as they die, 

 however, they begin to decay and reverse this process, absorbing 

 the oxygen and throwing off the gas, and should be at once mowed 

 and removed. They gather dust and harbor bacteria and various 

 injurious fungi; shade the soil and keep it damp and sour; while 

 certain species produce great quantities of pollen which is often 

 very irritating. Growing as they do where many children congre- 

 gate, the poisonous species, such as pokeweed, nightshade and jim- 

 son are very apt to be eaten. The three-leaved ivy, with its at- 

 tractive foliage and poisonous juices or exhalations, often occurs 

 along the borders of these city lots and causes blisters on the skin 

 of many a youngster. 



Instead of raising noxious weeds these vacant lots should be 

 put to more important uses. In most of the cities and larger 

 towns there are many poor people who would be glad to utilize 

 them for gardens. Such use would not depreciate their value for 

 building purposes and would greatly lessen the cost of living of 

 the needy and the amount necessarily bestowed in charity upon 

 them. In many places the weeds and rubbish can be removed at 

 a small cost, the surface leveled and sown to some perennial grass, 

 and the plot then used as a playground for children. Such play- 

 grounds are always welcomed in the crowded portions of the larger 

 cities, where open places for that romping and running so dear to 

 a child's heart and so necessary to its health, are often few or 

 absent. 



CLASSIFICATION OF WEEDS ACCORDING TO LIFE PERIOD. 



Weeds, like other plants, are grouped, according to the length 

 of time they live, into three classes, viz., annuals, biennials and 

 perennials. 



ANNUALS. An annual weed is one that rounds out its cycle 

 of existence within a single year. Of these there are two sub- 

 classes, ordinary or " summer annuals " and " winter annuals." 



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