94 



GROWTH OF PLANTS 



This dwarfishness in the seedUng may persist for weeks, months, or even 

 years or until some growth condition after-ripens a bud (generally a lateral 

 bud) so that it acquires vigor of growth. The most effective condition now 



Figure 32. Peach seedlings. Left: grown from non-after-ripened embryo. Right- 

 grown from after-ripened embryo. 



kno^\Ti for after-ripening such a bud is a period at low temperature. If 

 the dwarfed seedling is placed at 5° C (41° F) for six weeks and then placed 

 at a good growing temperature, one of the buds begins vigorous growth 

 similar to that sho^\Ti by the epicotyl of an after-ripened embryo. Fig. 33 

 shows a picture of a dwarfed seedling of Rhodotypos at two stages of 

 dwarfish growth and the later vigorous growth of the terminal bud. Lam- 

 merts '^^ has found that high temperatures will throw buds of the dwarfish 

 peach seedling out of dormancy and that the rate of elongation of such 

 buds is favored by a long day, especially by continuous illumination. 



From what has been said above, it appears that low-temperature strati- 

 fication does two things to dormant embryos: it overcomes the sluggish- 

 ness in their early growth and it after-ripens the epicotyl so that in its 

 later growth it forms a vigorous rather than a dwarfish plant above ground. 

 The epicotyl of the seed is, of course, a bud and the second phase of low- 

 temperature after-ripening described above is a phenomenon that occurs 



