RELATIVE STABILITY OF LIVING MATTER 



331 



is largely internal, but that the influence determining the direc- 

 tion of the growth is external, gravity (see Fig. 26, B). 



5. This " polar difference " is most energetic in j^flg-s terns, 

 gradually lessening in older growth, though the tendency remains 

 in quite old pieces. 



6. If internodes only are used, some plants will regenerate 

 and others will not ; but if they do regenerate, the tendency is 

 for roots to appear from the basal end and leaves from the apical, 

 whatever the position. 1 



7. If a piece of the root of a poplar be suspended vertically in 

 a moist chamber, apex downward, leaves and shoots will appear 

 from the basal? now the upper, end ; if suspended basal end 

 downward, the shoots will still arise from this (basal) end. 3 



8. Certain plants, as the begonia, are able to produce new 

 plants from even a single leaf'ii set in moist sand. In all cases, 

 so far as known, roots first arise at the base of the leaf stem, or 

 midrib section, and later shoots arise on the apical side of the 

 roots, whatever the position. 



9. Curiously, if the leaf be taken from a begonia just ready 

 to flower, the new plant will flower very quickly after becoming 

 established, but with few leaves and little growth ; but if it be 

 taken from a plant just out of flower, the growth will be greater 

 and the period longer before flowering follows. 



10. When pieces of stem are suspended vertically, apex up- 

 ward, polarity and gravity act together ; when suspended apex 

 downward they act oppositely. The two forces may, to some 

 extent, be separated by employing different positions. For ex- 

 ample, if the piece be held obliquely, apical end the higher, the 

 buds along the upper side will develop more than those on the 

 lower side ; and if it be placed horizontally, all the buds on what 

 is now the upper side of the stem will start, but those at the 

 apical end will grow more rapidly. 



If held in an oblique position with basal end higher, differ- 

 ent results follow ; but in general it is shown that where polarity 



1 Morgan, Regeneration, p. 74. 



2 It should be remembered that the basal end of the root is the end nearer 



the stem. 



3 Morgan, Regeneration, p. 75. 



