GERMINATION OF SEEDS 91 
To the inward sloping surface is pinned a seedling whose 
root has well started. The photograph (Fig. 84) shows 
that the root, con- 
tinuing to grow, has . 
turned from the ver- 
tical direction under 
the stimulus of the 
moisture in the bibu- 
lous paper, and is 
pursuing a general di- 
rection that is a re- 
sultant between the 
two stimuli. A more 
detailed observation 
of such an experi- 
ment shows that the 
root- tip sometimes 
turns toward and 
sometimes away from 
the moist paper. 
54. Escape of the 
cotyledons and _ the 
plumule.—After the wee 
hits be h Fic. 84.—A bean seedling showing the response 
root with its branches of the root when the stimulus of gravity is 
has anchored the from one direction and that of moisture from 
another. 
plantlet to the soil, 
the hypocotyl begins to elongate rapidly; and since the 
cotyledons are still within the testa this elongation results 
in the development of an arch, the hypocotyl arch (Fig. 
85). As the arch constantly seeks to straighten itself, the 
upward pull on the cotyledons finally draws them out of 
the testa and the hypocotyl straightens. The cotyledons, 
however, have done their work, and although they may 
become green and persist for some time, in the bean they 
are of no further importance. It is the escape of the 
