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; (8) 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 (Hrodium cicutartwm) 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. 
