SEEDS AND SEEDLINGS 



77 



to protect the delicate parts of the embryo from injury. The food 

 is in a form not easily dissolved by water or broken up by the 

 action of frost, so that it is kept in a hard state until such a time 

 as it can be softened by the process of digestion during the 

 growth of the plant. It can be seen that plants bearing seeds 

 having some of the above characters have a great advantage over 

 plants bearing seeds that are poorly protected. 



Milkweed fruit, showing method of seed dispersal. 



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

 have spent some time in the consideration of seeds simply to learn 

 a little about their structure. This has been done so that we 

 may understand the work as we take up, by means of the 

 following experiments, some of the factors which call the dormant 

 seed to life. We know that a dry seed, after lying dormant and 

 apparently dead for months and sometimes for years, will, when 



^ In making experiments it is important to exclude, if possible, all other factors 

 but the one you wish to determine. 



