INFLUEN-CE OF POLLEN'. 131 



than another of the same species, but no amount of nursing 

 or moving about will ever change a tender plant or animal 

 into a hardy one. But by introducing new elements, as 

 in cross-fertilization, we multiply the causes for wide 

 variation through the different hereditary characteristics 

 . of both parents. Then, by careful selection and propa- 

 gation of such crossrbred varieties as are worth preseiva- 

 tion, we are often able to secure those adapted to widely 

 different conditions, as seen among all of our long-culti- 

 vated and widely-disseminated plants. Why the seeds 

 from a plant should yield both tender and hardy varieties 

 can only be accounted for upon the hypotheosis that each 

 possesses transmitted hereditary characteristics, but what 

 the nature of the laws are that control this transmission 

 we know little or nothing. 



Plants that are indigenous, or have become naturalized 

 in cold climates and in elevated regions, are constantly 

 subjected to the loss of their leading shoots and branches 

 through the action of frosts and winds, and this being 

 repeated for centuries in succession, the plants at last 

 become permanently dwarfed, and this character becomes 

 fixed and hereditary, as seen in many of our cultivated 

 plants obtained from very cold or alpine regions. The 

 dwarf habit remains fixed in the individual, even when 

 cultivated in more favorable regions of a country, but so 

 soon as we commence to raise seedlings from these pig- 

 mies, we find that there is a tendency in a certain number 

 to grow taller than the parent plant, or to return to what 

 we may presume was the original form of the species. 



Porm and habit of plants are greatly modified by sur- 

 rounding conditions, and while severe winds and low 

 temperature may permanently dwarf plants in certain 

 countries or regions, high temperature and poor soils 

 may produce similar changes elsewhere. The Chinqua- 

 pin Chestnut {Castanea pumila), as found growing wild 

 over quite extensive regions in some of our Southern 



