668 SUMMAKY AND Chap. XIL 



upwards through 109° in 3 h. 8 m. The after-effects 

 of apogeotropism last for above half an hour ; and 

 horizontally-lai.l hypocotyls are sometimes thus car- 

 ried temporarily beyond an upright position. The 

 benefits derived from geotropism, apogeotropism, and 

 diageotropism, are generally so manifest that they 

 need not be specified. With the flower-peduncles of 

 Oxalis, epinasty causes them to bend down, so that 

 the ripening pods may be protected by the calyx 

 from the rain. Afterwards they are carried upwards 

 by apogeotropism in combination with hyponasty, and 

 are thus enabled to scatter their seeds over a wider 

 space. The capsules and flower-heads of some plants 

 are bowed downwards through geotropism, and they 

 then bury themselves in the earth for the protection 

 and slow maturation of the seeds. This burying 

 process is much facilitated by the rocking movement 

 due to circumnutation. 



In the case of the radicles of several, probably of all 

 seedling plants, sensitiveness to gravitation is confined 

 to the tip, which transmits an influence to the adjoining 

 upper part, causing it to bend towards the centre of 

 the earth. That there is transmission of this kind was 

 proved in an interesting manner when horizontally 

 extended radicles of the bean were exposed to the 

 attraction of gravity for 1 or l^^ h., and their tips were 

 then amputated. Within this time no trace of curva- 

 ture was exhibited, and the radicles were now placed 

 pointing vertically downwards ; but an influence had 

 already been transmitted from the tip to the adjoining 

 part, for it soon became bent to one side, in the same 

 manner as would have occurred had the radicle 

 remained horizontal and been still acted on by geo- 

 tropism. Eadicles thus treated continued to grow out 

 horizontally for two or three days, until a new tip was 



