Epinasty and Hyponasty of Raphanus Cotyledons. 369 



Before the cotyledons are 96 hours old, however, they will close 

 if illumination is directed toward the notch. This may be as- 

 signed to hyponastic curvature of the hypocotyls. 



It might seem as if this is a wise protection for the tender 

 epicotyl. With this is to be correlated the fact that in total dark- 

 ness a certain period of time elapses before epinastic curvature 

 of the hypocotyl takes place. 



When we consider the cultures in which the organs under 

 consideration were exposed to varying conditions, as in Nos. 6 

 and 7, we find that a broad field of investigation opens out be- 

 fore us. Let us first look carefully at No. 6. 



After 66 hours we find that by 18 hours exposure to total 

 darkness the cotyledons become changed from a strongly epinas- 

 tic to a hyponastic condition. This seems to show that the ab- 

 sence of light in this case is favorable to a hyponastic position. 



After 108 hours, the cotyledons being at that time hypo- 

 nastic, they were placed in strong illumination for 6 hours. At 

 the end of this period they were placed in dark for 12 hours, 

 then in diffuse light. Not until this latter change took place did 

 the cotyledons show any marked epinastic curvature. This, and 

 the peculiar appearance of the cotyledons in the two succeeding 

 states have led me to think that we have here a manifestation 

 of a latent period of growth with respect to epinastic curvature. 

 It is peculiar that when this epinastic condition was obtained 

 the absence or presence of light should have no further effect 

 on the cotyledons. 



With respect to No. 7, it is only necessary to point to the 

 difference in the results. In the latter we have without doubt 

 a set of changes which instead of tending towards fixation of 

 position, tend in exactly the opposite way, /. e. toward extreme 

 irritability. It has now become apparent that what is needed is 

 accurate permutations of these conditions, varying the time to 

 secure results which explain the phenomena noted in this paper. 



That the influence of light upon dorsiventral organs which 

 produces epinastic or hyponastic growth is dependent on the in- 

 tensity of light-vibrations is beyond a doubt. To determine the 

 intensity of vibrations required to produce a given curvature, and 

 to solve some of the problems indicated by these notes is the ob- 

 ject of further experiments being conducted at the University. A 

 series of permutations are now under way and an effort will be 

 made to cover as much of the debated ground as possible. 



February 3, 1891. 



