

L 



Extreme modification of development by photoperiodism in the common weed 

 Chenopodium rubrum. Right, a plant germinated and grown under 8-hour photo- 

 periods; much of the bulk of the 3-week-old seedling consists of flower parts. 

 Left, a plant germinated and grown under 20-hour photoperiods; after more 

 than 3 months, it remains completely vegetative. (Right-hand photograph from 

 Cumming [1959], by permission of the editors of Nature; both photographs 

 courtesy of Dr. B. G. Cumming of the Canada Department of Agriculture.) 



