6 DWAEF AND SLOW-OBOWINO CONIFERS 



1. Probably the largest number of such forms have 

 occurred in the seed beds of nurseries. Some conifers vary 

 enormously from seed, and with species like Ptcea excelsa, 

 which has been long known and frequently raised from 

 seed, new forms are constantly appearing, showing varia- 

 tion in colour, height, and habit. When dwarf forms 

 originate in this manner, they usually retain their habit 

 irrespective of age. 



2. Other dwarf forms result from environment. The 

 self-sown seedlings of conifers on the higher mountains 

 and in cold countries have naturally a harder fight for 

 existence, and become stunted, and the more inhospitable 

 and wind-swept the locality the smaller the trees become, 

 until at length one gets either a prostrate shrub flat on 

 the ground, such as the arborescent Juniperus virginiana 

 becomes on the gale-swept cliffs of the coast of Maine in 

 U.S.A., or else a low dense shrub, such asPinus cembra — 

 the Arolla Pine of the Swiss Alps — becomes in its stunted 

 Siberian and Japanese representative, Pinus pumila. 

 Such forms, notably stunted forms of the common juniper, 

 occasionally revert to normal in lowland cultivation. 



3. Other dwarf forms have originated from sports on 

 branches of an otherwise normal arborescent tree. Most 

 people have at some time noticed those curious nest-like 

 conglomerations of branchlets that occur at times on trees, 

 and are familiarly known as " witches'-brooms." These 

 are said to arise from several causes, either from some 

 insect irritation or some constriction of sap ; but whatever 

 be the cause, the result is the abnormal mop-head-like 

 growth, and it has been found that cuttings or grafts taken 

 from such growths produce plants similar to the broom. 

 Such plants, however, especially grafted plants, at times 

 revert to normal trees. Examples of dwarf forms raised 

 from such brooms are Picea excelsa, var. tabulifonnis, and 

 Pinus Sylvestris, var. Beauvro7iensis. 



These natural dwarfs are the forms with which we are 

 concerned. 



