150 BOTANICAL GAZETTE [august 



the barrier of siliceous rock upon the adjacent mainland. His view that "the 

 Canadian cedar swamp is, then, a phase of Warming's calcareous low-moore" 

 appears less probable, and does not seem to explain the frequent presence of 

 Thuja in associations with Larix in bogs. 



It would seem to remain for some one possessing intimate knowledge of 

 the northern forests, but without prejudice for or against the chemical theory of 

 soil control, to harmonize such opposing views as those of Hutchinson and 

 Fernald, by showing that each contributes to the solution of a complex 

 problem, and that the truth lies at neither extreme. — Geo. D. Fuller. 



Hybrid vigor. — This subject is brought up to date and ably discussed by 

 JONESi in the publication of his latest experiments with corn. The author 

 has continued the inbreeding experiments started by East and Hayes. As 

 was predicted, the inbred strains have now reached a condition of almost 

 complete homozygosity, so that further inbreeding no longer brings decrease 

 in vigor, and crossing within the strain brings no increase. The author 

 amplifies somewhat his previously published^ interpretation of hybrid vigor 

 on the basis of dominance of linked factors. 



In addition to the main thesis, some very interesting by-products are 

 discussed. As a practical method of utilizing hybrid vigor in corn, Shull* 

 and others have advised isolating strains A and B and using for seed corn every 

 generation the Fi grains produced hy AXB. A disadvantage of this method 

 lies in the fact that these seeds are usually small, for, although they contain 

 an Fi embryo, the amount of endosperm is that of the maternal parent (from 

 an inbred, "non-vigorous" race, A or B). Since these seeds are small, the 

 Fi individuals get a poor start, limiting their expression of hybrid vigor. To 

 overcome this difficulty Jones proposes an intelligent use of 4 selected strains 

 thus: AXB giving AB; CXD giving CD; ABXCD giving the seed corn to 

 be used, which will have sufficient endosperm for a good start and will display 

 hybrid vigor as well. 



Carrying further his experiment^ with mixed foreign and own poUen 

 ("yellow" and "white" poUen), Jones attempted to discover whether there 

 was any selective fertilization in favor of the foreign pollen; this might have 

 been expected from the advantages which foreign pollen brought, as well as 

 from the weU-known behavior in self-sterile races. The residts, however, 

 pointed consistently in the opposite direction; own pollen was slightly but 



^ Jones, D. F., The effects of breeding and cross-breeding upon development. 

 Conn. Exper. Sta. Bull. 207. pp. 100. pis. 12. 1918. 



s Box. Gaz. 56:70-72. 1918. 



* Shull, G. H., Hybridization methods in corn breeding. Amer. Breeders Mag. 

 1:98-107. 1910. 



1 Jones, D. F., Bearing of heterosis upon double fertilization. Box. Gaz. 

 65:324-333- figs- 3- 1918. 



