1912] Goodspeed: Nicotiana Hybrids 141 



still green and the fourth flower only was in the proper con- 

 dition to be measured. On September 30 there were, in addi- 

 tion, four newly opened buds. The next measurements on this 

 plant are dated October 2, on which date four flowers were 

 measured — i.e., three of the four that were newly opened buds 

 on the 30th and one which had come to maturity since that time. 



In other words, when the measurements were finished on each 

 day, only small buds and immature flowers were left on the 

 plants. By taking the measurements every other day there was 

 usually an abundance of material and most of it in the same 

 condition. The foregoing applies, of course, to measurements 

 on the parent as well as on the hybrid flowers. 



Plate 31 gives the number of flowers measured on sixteen 

 or seventeen different days, between October 1 and November 8, 

 on single plants of the various groups and. in the ease of the 

 plotted figures in the upper right hand corner, the number of 

 flowers measured on all the plants of the group representing the 

 cross I5X II c^- The plant upon which the greatest number of 

 flowers was measured during the five weeks is, in each case, given. 

 The close similarity between the plotted figures is rather striking. 

 Climatic conditions (see page 124), operating on all the plants, 

 undoubtedly is the chief cause of this similarity, though a 

 probable periodicity in the production of reproductive parts, as 

 opposed to those strictly vegetative, may enter in as a factor. 

 It hardly seems, however, that this last can have great signifi- 

 cance in reference to the similarity between the plotted figures, 

 since all the plants would not naturally be influenced by such 

 a periodicity on practically the same dates. Between October 

 20 and 30, when the production of flowers was in general ex- 

 ceedingly low, there had been rain, cloudy weather and an 

 extremely low temperature at night, following a period of 

 climatic conditions practically the reverse. Probably the direct 

 result, in this connection, was seen in a tendency throughout to 

 drop the flower buds. j\Iore favorable weather conditions — Nov- 

 ember 1 to November 8 — always caused an immediate and rather 

 disproportionately large increase in the production of flowers. 



The degree of variation in corolla diameter among the hybrid 

 plants is. ill each ease, large. For example. III^X I c^ varies 



