MONOGRAPH OF THE GENUS PYRUS. 189 



since pear varieties are of the lowest grade, incapable of pro- 

 pagating fruit by close-fertilization, and therefore wholly un- 

 likely to impress by their pollen any characteristic upon the 

 pericarp of another variety.^ A large part of the Introduc- 

 tion is occupied with further evidence that the Pear-trees of 

 cultivation are all of one species, from which have proceeded 

 six races, completely fertile hiter se, and varieties ad infinitum. 

 In this respect the Pear-tree has but followed the example of 

 most fruit and fruit-trees, and of the Grains, etc., which had 

 apparently diverged into races, or distinct but closely related 

 types, in very early times, and those under cultivation have 

 themselves varied and subdivided more and more. Finally, 

 M. Decaisne maintains, seemingly with good reason, that to 

 combine into one genus the Apple, Pear, Quince, Sorb, and 

 Mountain Ash, as done by Linnaeus and followed by the latest 

 authorities, is to misconceive the laws of the natural system ; 

 that " to unite generically these plants, which differ in the 

 character of their wood, the vernation of their leaves, their 

 inflorescence, the aestivation of the corolla, and the structure 

 of their fruit," logically leads to the combination of all Po- 

 macece into one genus. He accordingly restricts the genus 

 Pyrus, or (restoring the classical orthography) Pirus, as did 

 Tournefort and Jussieu, to the Pear proper. To the organo- 

 graphy of this restricted genus, from the wood to the embryo, 

 a full chapter is devoted. In the course of this the relative 

 systematic value of characters observed is brought out. He 



^ Yet the Apple, which is iu the same case, does so. An interesting 

 instance of this kind lately came under our notice, an apple from a Spitz- 

 enberg tree, one half (at least as to the surface) Spitzenherg, the other 

 half Russet. A tree of the latter fruit stood about 200 yards off. Several 

 cases of this sort are known, in which, as in this, the division is into two 

 exactly equal parts of the circumference, and the line of demarcation 

 abrupt. This is quite unexpected, as the Secretary of the Smithsonian 

 Institution, who sent us the fruit, remarked ; for as the styles and carpels 

 were five, we should have expected the division to be into fifths, and ac- 

 cording to the number of the stigmas which were acted upon by the for- 

 eign pollen. It is, moreover, to be noticed that the action of the pollen 

 in this case is manifest upon what is morphologically the calyx, not upon 

 the pericarp. The apple we refer to was grown in the orchard of William 

 Wicksham, of Washington County, Pennsylvania. — A. G. 



