no 



GROWTH OF PLANTS 



for coat changes and a winter for embryo after-ripening. Fig. 41 illustrates 

 this behavior. Seeds of C. rotmidifolia were planted in flats m the tall ol 

 1932 and placed in three sorts of cold frame at Yonkers. Row A shows 

 photographs of these flats in June of 1933 after one winter m soil. None 



MULCH 



BOARDCOVER 



OPEN 



GREENHOUSE 

 21° C 





■f 



«11:3^'- 



54 % 



Figure 41 Per cent germination of various Crataegus seeds when planted m the fall 

 of 1932 and placed in various cold frames. A and B, C. rotundifolia photographed June, 

 1933 and July, 1934 respectively. C, C. flava photographed July, 1934. 



has germinated. Row B shows photographs of the same flats in July of 

 1934. Row C shows the seedling production for C. flava the second spring 

 after fall planting in flats in cold frames. No seedlings of either species 

 were produced when the flats were kept continuously in the greenhouse. 



Fig. 42 shows that seeds of three of these more resistant species^ of 

 Crataegus A\all not germinate after five or even nine months in soil at 5° C 

 (41° F) followed by six weeks at good growing temperature. They all give 

 abundant seedling production if the flats are kept four months at 21° C 

 (70° F), then at 5° C (41° F) for five months followed by six weeks at a 

 higher temperature. In these the four-months' period of high temperature 

 can be shortened to two or three weeks by decomposing the coats partially 

 with concentrated sulfuric acid before the high-temperature period. By 

 such treatment the total high- and low-temperature after-ripening periods 



