71 



A valuable historical review, entitled " The Founders of the Art of Breeding,'* by- 

 Herbert F. Roberts, will be found in Journal of Heredity, x, 99, 147 (March and April 1919). 



After giving due credit to Koelreuter and others for their pioneer work in regard 

 to sexuality in plants, he draws attention to what he terms " the revelations of 

 Sprengel," who published (in German) his work " The Newly Revealed Secret of Nature 

 in the Structure and Fertilisation of Flowers " (Berlin, 1793). It was Sprengel's chief 

 merit to discover the fact of insect fertilisation. Roberts goes on to say that to 

 Sprengel we owe the discovery of dichogamy, i.e., the maturing of the stamens and 

 pistils of flowers at different times. His conclusion that Nature, in most cases, intended 

 that flowers should not be fertilised by their own pollen, and that the peculiarities of 

 flower structure can only be understood when studied in relation to the insect world 

 were revolutionary for his time. Roberts proceeds to point out that it remained for 

 Darwin to show how the results from such perpetual crossings are limited and held in 

 check by the operation of natural selection. And not long afterwards (though neglected 

 for a generation) came the work of Mendel, and then the scientific age of plant-breeding 

 and the development of " genetics." 



Dr. D. T. MacDougall's paper (" Hybridisation of Wild Plants," Bot. Gaz., lxiii, 



45, 1907) begins— 



The number of forms of plants which have been or are regarded as hybrids by systematists is a 

 large one and includes several oaks, of which two have been examined during the last two seasons. 

 Attention has been called previously to the untrustworthiness of the custom prevalent among botanists 

 of attributing a hybrid origin to certain plants because they appear to exhibit halved, fused characters, 

 or a mosaic of qualities derived from the two supposititious ancestors. In some instances such deductions 

 have been made by which the ancestry of a questionable plant has been made to include three or even 

 four species. The argument of distribution is the main one offered in such attempted demonstrations. 

 In many cases this, together with other circumstantial evidence, may amount to almost positive conviction, 

 but unless this close relation of well-joined facts is furnished, assertions as to the hybridity ©fa plant must 

 be taken simply as a suggestion to be tested by cultural or experimental methods. 



He points out — 



The reformation of a hybrid by the cross-pollination of the parents to which it may be ascribed is 

 by no means simple in all instances, nor is it always easy of accomplishment. In the first place, the original 

 cross-pollination may have taken place possibly under an exceedingly rare combination of favourable 

 physiological conditions difficult to secure or duplicate in experimentation. 



Dr. MacDougal's own experiments to illustrate his paper are based on Quercus, 

 and it concludes with references to a large number of natural plant hybrids of North 

 America, based on a list originally prepared by Dr. David George. It takes cognisance 

 of 117 hybrids distributed over twenty-four families. The paper is most suggestive. 



See also A. R. Rolfe's remarks on hybridisation in Orchids (Orchid Review, 1916, 

 1917). 



Although the number of artificially produced hybrid trees is small, compared to the number of 

 crosses among other species, several noteworthy trees have been described from time to time which do not 

 conform to any known kinds, and they have been attributed to an assumed hybrid ancestry. 



Then follows a select list of trees which " have been regarded upon reasonably 

 good evidence as natural hybrids." The whole paper, on a Hybrid Catalpa is well 

 worth study. (Jones and Filley in Journal of Heredity, January, 1920, p. 16.) 



