74 



SEEDS AND SEEDLINGS 



which we come most in contact in daily hfe. Many of our garden 

 vegetables, peas, beans, squash, melons, etc., all of our great hard- 

 wood forest trees, beech, oak, 

 birch, chestnut and hickory, 

 used for the ' trim ' of houses, 

 all of our fruit trees, pears, 

 apples, peaches, and plums, 

 and, in fact, a very large 

 proportion of all plants living 

 in the north temperate zone 

 are dicotyledons. 



A third type of plant, 

 grouped according to the 

 number of cotyledons, is the 

 group called the polycoty- 

 ledons, represented by the 

 pines and their kin. Such 

 plants furnish most of the limiber and shingles used in the con- 

 struction of frame houses. The soft woods (as the pines, hemlocks, 

 spruces, and other " evergreens ") are also of much value in the 

 manufacture of paper. The wood-pulp industry has grown to 

 such proportions as to be a menace to our softwood forests. 



Problem XI. A study of the factors necessary for awakening 

 {g6Tnninatin£) tlxe embryo within the seed. (Laboratory Man- 

 ual, Prdb. XI.) 

 (a) Moisture, 

 ih) Teynperature. 

 (o) Oxygen. 

 Ad) Food. 



A spruce cone ; the seeds are held under the 

 scales of the cone, one of which is shown 

 removed. 



External Factors which determine the Growth of Seeds.^ — We 

 know that a dry seed, after lying dormant and apparently dead 

 for months and sometimes for years, will, when the proper stimuli 

 are apphed to it, start in its growth into a new plant. Something 

 from outside the seed must evidently start the growth of the httle 

 embryo within the seed coats. There are several factors which 



' In making a series of experiments it is important to keep the conditions uni- 

 form, varying only the one we are testing. 



