30 Process of Fertilization: Distribution of Tree Seeds. 



and the hybrids thus obtained may, in the case of trees, be perpet- 

 uated by layers, cuttings or grafts. 



121. When fer- 

 tilization is 



se- 

 cured, the stami- 

 ntite blossoms fall 

 off or dry up, and 

 the germs at the 

 base of the pistils 

 expand, and ripen 

 into the fruit. 

 This usually hap- 

 pens the same 

 year that the blos- 

 soms appear, but 

 in some of the 

 oaks and the con- 

 ifers, the ripening 

 process is not com- 

 pleted till the au- 

 tumn of the sec- 

 ond year after fer- 

 tilization takes 

 place. Many trees 

 have their fertile 

 and their sterile 

 years; indeed, but 

 few trees bear 

 steadily and alike from year to year. In the case of trees intro- 

 duced into regions where they are not native, they may thrive and 

 grow to large size, but without ever bearing fertile seeds, or even 

 without blossoming. A dense shade is unfavorable for the forma- 

 tion of seeds, and trees, after being exposed to the air and light by 

 the clearing away of trees around them, will usually bear fruit more 

 abundantly in first or second year after. 



Of die Natural Distribution of Forest Tree Seeds. 

 122. While the seeds of all trees may fall and take root under or 

 near the parent tree, and there thrive, when properly supplied with 



13. Alnus glutinosa Alder. 



