17-1 POPULUS. 



in motion by a very slight breath of air. The buds of 

 many species, particularly those of Pop. balsamifera and 

 Pop. Canadensis, are protected and varnished with a strong 

 but agreeably-scented gummy matter, much sought after 

 by honey-bees, who convert it into the substance called 

 propolis, with which they stop chinks and cement their 

 hives to the boards upon which they stand. 



The species delight in a rich, moist soil, or in the neigh- 

 bourhood of running water, but they do not thrive in marshes 

 or soils saturated with stagnant moisture. Hitherto the 

 male plants only of many exotic kinds have been introduced, 

 so that no opportunity has existed of raising plants from 

 seed; their propagation, therefore, is continued by means 

 of cuttings and layers, and in some species by the suckers 

 thrown up from the superficial roots. Considerable con- 

 fusion appears to exist in regard to the species and va- 

 rieties, and these difficulties are not likely to be solved 

 till both sexes of the different kinds have been cultivated 

 together, and their produce tested by experiment ; on this 

 account, we shall treat the various kinds to be described, 

 as species, although Loudon deems some of them mere 

 varieties, and even thinks that all the kinds now cultivated 

 in Britain may be referred to and included under the 

 generic heads of Pop. alba, Pop. tremula, Pop. nigra, and 

 Pop. balsamifera. 



The Poplars afford nourishment, both by their leaves 

 and wood, to a great variety of insects in the larva as 

 Avell as in the perfect state, but as notice will be taken 

 of those most interesting for their beauty or rarity, when 

 describing the different species, we omit any detailed 

 enumeration of them at present. 



