124 Jean White: Red Wood in Conifers. 



As in some of the above cases, the parts of the ?tem which 

 were equally darkened were subjected to unequal pressure or 

 tension, due to the curving round of the branches experimented 

 upon, the thicknes,s of the tracheide walls in red and white wood 

 was the saaiie, it seems to be improbable that pressure and ten- 

 sion of the intensity produced by forcibly curving the branch, 

 exert any pronounced influence on either the thickness of the 

 walls, diametei' of the tracheides, or formation of red wood. The 

 latter is purely a response to gravity, and is only accompanied 

 by an increase in the thickness of the walls when the red wood 

 side is the more strongly illuminated one, which is unusual. 

 The minimal period for perception and response, as tested by the 

 method of summation, is two hours. Exposures to gravity of 

 less than two minutes' duration produce no permanently lasting 

 effect. 



In conclusion, I wish to record my sincei'e thanks to Prof. 

 Ewart for his assistance, and also for allowing me the use of the 

 Botanical laboratory at the Melbourne University. 



