CHAP. III. OF THE EADICLE OF ZEA. 179 



to the continued irritation from the card, two complete 

 loops, that is, a helix of two spires ; which afterwards 

 became pressed closely together. Then geotropism 

 prevailed and caused the apex to grow perpendicularly 

 downwards. In another case, shown at (D), the apex 



Fig. 69 



.0 D. 



Zea mays : radicles excited to bend away from the little squares of card 

 attached to one side of their tips. 



in making a second turn or spire, passed through the 

 first loop, which was at first widely open, and in 

 doing so knocked off the card ; it then grew perpen- 

 dicularly downwards, and thus tied itself into a knot, 

 which soon became tight ! 



Secondary Radicles of Zea. A short time after the 

 first radicle has appeared, others protrude from the 



