74 



SEEDS AND SEEDLINGS 



A spruce cone ; the seeds are held under the 

 scales of the cone, one of which is shown 

 removed. 



which we come most in contact in daily life. 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 lumber 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 

 (germinating the embryo within the seed. (.Laboratory Man- 

 ual, Prob. XlS 



(a) Moisture. 



(&) Temperature. 



(c) Oxygen. 



(#) Food. 



External Factors which determine the Growth of Seeds. 1 We 

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

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

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

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

 embryo within the seed coats. There are several factors which 



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

 form, varying only the one we are testing. 



