28 PRACTICAL COURSE IN BOTANY 



19. Do you find any edible seeds without protection? If so, account 

 for the want of it. (21, 22.) 



20. Name some of the agencies that may assist in covering seeds with 

 earth. 



21. Do you know of any seeds that bury themselves? 



22. The seeds of weeds and other refuse found mixed with grain sold 

 on the market are known, commercially, as " screenings." Wheat brought 

 to mills in Detroit showed screenings that contained, among other things, 

 seeds of black bindweed, green foxtail grass, yellow foxtail, chess, oats, 

 ragweed, wild mustard, corn cockle, and pigweed. Can you mention some 

 of the ways in which these foreign substances may have gotten into the 

 crop and suggest means for keeping them out ? 



Field Work 



The subjects treated in the foregoing chapter are, in general, better 

 suited to laboratory than to field work. There are some details, however, 

 which can be observed to advantage out of doors. Many of the seeds 

 found in your walks will show peculiarities of shape and external markings 

 and color that will invite observation. Examine also the contents of dif- 

 ferent kinds you may meet with, as to the presence or absence of endosperm 

 and the arrangement and development of the embryo. Note: (1) whether, 

 as a general thing, there is any difference in size and weight and amount of 

 nourishing matter in the two kinds ; (2) the greater variety in the shape 

 and arrangement of the cotyledons in the albuminous kind, and in the ar- 

 rangement of the embryo ; (3) the differences in the development of 

 the plumule in the two kinds, and give a reason for the facts observed. 



Among the different seeds you may find, look for adaptations for dispersal, 

 and decide to what particular method each is suited. Study the agencies 

 by which various kinds may get covered with soil. If the common stork' s- 

 bill (Erodium cicutarium) grows in your neighborhood, its seeds will well 

 repay a little study, and if there is a field of peanuts within reach, do not 

 fail to pay it a visit. 



