280 PRINCIPLES OF PLANT CULTURE 



inches and 6 inches from the bottom ; place the pots in 

 a warm place for 3 weeks, after which carefully remove 

 the soil, noting the germination of the seeds in the dif- 

 ferent layers. 



Vigor of plantlet proportionate to size of seed (48) . - 

 Plant large and small specimens of navy beans by them- 

 selves, in greenhouse saucers, and permit them to ger- 

 minate. The smaller seeds usually germinate earlier 

 than the larger, but they produce more slender plant- 

 lets, which soon fall behind the others in development. 



Plantlet visible in the seed (53). Boil samples of 

 various kinds of seeds until they are fully swollen, after 

 which require the students to dissect them and to seek 

 out the plantlets. Lenses, needles and forceps are very 

 useful in this work. 



The cotyledons a storehouse for food (59) . Remove 

 the cotyledons of some bean plantlets growing in a flower 

 pot or saucer, leaving those of other plantlets intact. 

 After a week note the result in the checked growth of 

 the mutilated plants. 



Vascular bundles (67) . Study these as shown in the 

 stalk of Indian corn, in the leaf stems of various plants 

 and in the leaf scars on the stems of plants. 



Cambium layers (68). Locate these in sections of 

 various dicotyledonous stems, including the potato tu- 

 ber ; also note the absence of the cambium layer in 

 monocotyledonous stems. 



Root-hairs (100). Study these as illustrated when 

 seeds germinate in the seed tester. Germinated radish- 

 seeds, left in the seed- tester two or three days, usually 

 develop root-hairs in great abundance. Also search out 

 the root-hairs in potted plants. Emphasize the differ- 

 ence between root-hairs and root branches. 



