110 THE AMERICAN MONTHLY [Apr 



BIOLOGICAL NOTES. 



L. H. PAMMEL. 

 Hybrid Citrus. — Mr. H. J. Weber,of the U. S. Depart- 

 ment of Agriculture, presented some interesting facts con- 

 cerning Citrus hybridization caused by polyembryony 

 at a recent meeting of the Society of Plant Morphyology 

 He has shown from many observations and comparisons 

 of the foliage characteristics of the hybrids that where 

 two or three seedlings were developed from a single seed 

 they not infrequently showed marks of foliage differen- 

 ces. It is well-known that most species of the genus 

 Citrus are commonly polyembryonic. A single seed of a 

 common orange has been known to produce as high as 

 thirteen seedlings. The adventive embryos develop di- 

 rectly from the mother tissue and the writer says, "we 

 should not expect to show any of the characteristics of 

 the male parent. This was the conclusion reached by Mr. 

 Swingle, and the writer jointly in discussing the matter 

 several years ago, and the development of the hybrids has 

 now shown this to be the case. In several instances in 

 hybrids of Citrus aurantium, which has unifoliolate leaves, 

 with C. trifoliata, which has trifoliolate leaves, where the 

 former was used as a female parent, two or three seed- 

 lings have been produced from the same seed; one of 

 which had trifoliolate leaves and the others strictly uni- 

 foliolate leaves exactly like those of the mother parent. 

 In such cases it is evident that the trifoliolate seedling 

 inherits this character from the male parent and that the 

 embryo from which it grew was developed from the egg 

 cell proper. The other seedlings in such cases, having 

 unifoliolate leaves like the mother parent, are doubtless 

 developed from the so-called adventive embryos." 



Tubercular Infection. — The Messrs. Lannelonge and 

 Achard have made a series of experiments to determine 

 the different channels through which animals may take 



