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THE AMERICAN NATURALIST [Vol. LI 



By thus inserting letters in the hybrid number, to desig- 

 nate the second and third plants, we indicate the vegeta- 

 tive origin of these plants, and also their quasi-sib rela- 

 tion to the true hybrid. 



Open pollination, or lack of protection of flowers in gen- 

 eral, can be indicated in the numbers, if this seems de- 

 sirable, by underscoring the proper letter or number, — 

 the use of two letters with the series number for hybrids 

 making it possible to do this with the pollen parent as well 

 as with the seed parent. 



An incidental advantage over the original plan results 

 from the use of letters with the series number in the way 

 here indicated. This consists in the fact that the numbers 

 for hybrid and non-hybrid series are thus made s>Tn- 

 metrical in relation to the number of generations involved. 

 As an illustration we may take the case of the Matthiola 

 cross mentioned above. This cross was made in 1914, and 

 the hybrid seeds were planted, together with seeds from 

 self ed parents of the same types, in 1915 and 1916. Corre- 

 sponding to the Fi hybrids 23ea-l, etc., we have the Fj 

 selfed progeny 19a-l, etc., from a Snowflake parent, and 

 25c-l, etc., from a Slender parent, while by the original 

 method these three numbers might be 23Grl, 19-1-1, and 

 25-3-1. 



As will readily be seen, this scheme is elastic ; if the five 

 main features stated above are adopted, different workers 

 may add, modify, or omit various details, and still use 

 numbers intelligible to each other with little or no special 

 explanation. Further, the method of designating series 

 and initial individuals is essentially independent of the 

 other features suggested, so that any of the latter features 

 may be adopted without the former. 



All the schemes so far discussed give cumulative num- 

 bers, which include the whole pedigree from the Pj indi- 

 viduals down. ShuU (1908, pp. 59-64) has described a 

 non-cumulative system, in which individuals have only 

 temporary numbers (in the field depending on row and 

 position in row) until selected as parents. Each parent 



