90 UrWARD GROWTH OF THE HEAD, AND pt. ir. 



their elongating only at their ends, and to their not 

 being thrust bodily through the earth. I have laid 

 horse-chestnuts on the surface of a box of earth, and, 

 by arching them over with layers of damp flannel 

 which did not touch them, they grew, and the tap- 

 roots struck downward into the earth and fixed them- 

 selves ; though they had no foreign fulcrum to press 

 from, except the weight of the seed, which was not 

 perpendicularly above them. Can there be anything 

 glutinous about the silver ends of roots, which enables 

 them to adhere to the earth while their new growth is 

 protruded through it ? And I may ask here, if roots 

 have spongioles or small sponges at their ends, are 

 we to believe that these sponges are locomotive or 

 stationary ? Are we to believe that these delicate 

 organs are thrust forward through the hard ground ? 

 Or are we to suppose that the perpetual new growth 

 of root is perpetual new sponge, as its preceding 

 sponge is converted into root ? 



As the stems of the plants grew, I heightened the 

 moist canopy, and let in light only by one opening. 

 All the stems grew towards that opening ; and as often 

 as the opening was changed from one end of the 

 canopy to the other, the direction of the stems was 

 changed ; that is, besides the new growth towards the 

 hght, the parts of the stems which were already 

 formed were bent towards the light. Three or four 

 hours were sufficient to effect this change in these 

 tender, drawn stems. 



