94 



UPWARD GROWTH OF THE HEAD, AND pt. ir. 



to double back ; and in doing so I have known the 

 root grow spirally up the narrow tube like a cork- 

 screw, and having at last (from becoming thin) turned, 

 grow straight down through the screw. The tube 

 being then quite filled up, the side-fibres of the upper 

 end of the root grew straight up in a bunch. In 

 plants which have overgrown their pots, the roots may 

 be seen to grow straight up the side of the ball of 

 earth, and in all directions around it, owing to the 

 mechanical confinement in the pot. But I do not 

 think that the roots ever return through the ball of 

 earth towards the plant. The want of hght may 

 probably be considered a sufficient reason for branches 

 never returning towards the stem. I think it more 

 difficult to find a reason for this perpetually centrifugal 

 (or, if nova reruni iiomina be allowed, ipsifugal) 

 determination of the root, 

 strong In all the cases in all these experiments the plants 



downward 



«on o^f'tap permanently, and independently of their seeds, 



probawe Iii t^^^ cascs whcrc the gemmules or stems came 



ganiJ^tioi down into the air they grew across the wires to the 



of it. 



light at the window. None came from under the 

 flower-pot on the sides towards the room, even though 

 they emerged from the earth close to those sides. 

 And in all cases, whether the gemmule grew upward 

 through the earth, or downward into the air, the first 

 or tap-root showed itself from above below, and never 

 turned upward. But the branch-roots fixed them- 

 selves, and grew from below upward ; and I therefore 



