PLANT-BREEDING METHODS 



421 



hands off. Or a strong wind may succeed in forcing into the greenhouse 

 seeds of the same species as the one undergoing investigation. Or pests 



FIG. 170. Birdproof cereal breeding garden at the University of California. 



FIG. 171. Pedigree cultures of Bursa in greenhouse of the Department of Botany, Prince- 

 ton University. (Photo from G. H. Skull.) 



of various sorts may appear damping off, insect pests, snails, slugs, mice, 

 and in the breeding garden birds, gophers, moles, rabbits, etc. In this 

 connection it may be sufficient to say that eternal vigilance is the price 



