178 SENSITIVENESS OF THE APEX Cuap. UI. 



on it. There were therefore only 10 out of the 68 

 which certainly were not acted on. Some of the 

 radicles which were experimented on were young and 

 short, most of them of moderate length, and two or 

 three exceeded three inches in length. The curva- 

 ture in the above cases occurred within 24 h., but it 

 was often conspicuous within a much shorter period. 

 For instance, the terminal growing part of one radicle 

 was bent upwards into a rectangle in 8 h. 15 m., and 

 of another in 9 h. On one occasion a hook was 

 formed in 9 h. Six of the radicles in a jar containing 

 nine seeds, which stood on a sand-bath, raised to 

 a temperature varying from 76° to 82° F., became 

 hooked, and a seventh formed a complete loop, when 

 first looked at after 15 hours. 



The accompanying figures of four germinating seeds 

 (Fig. 69) show, firstly, a radicle (A) the apex of wliich 

 has become so much bent away from the attached 

 square as to form a hook. Secondly (B), a hook 

 converted through the continued irritation of the 

 card, aided perhaps by geotropism, into an almost 

 complete circle or loop. The tip in the act of forming 

 a loop generally rubs against the upper part^ of the 

 radicle, and pushes off the attached square ; the loop 

 then contracts or closes, but never disappears ; and 

 the apex afterwards grows vertically downwards, being 

 no longer irritated by any attached object. This 

 frequently occurred, and is represented at 0. The 

 jar above mentioned with the six hooked radicles and 

 another jar were kept for two additional days, for the 

 sake of observing how the hooks would be modified. 

 Most of them became converted into simple loops, 

 like that figured at C ; but in one case the apex did 

 not rub against the upper part of the radicle and thus 

 remove the card; and it consequently made, owing 



