CHAP. X. APOGEOTROPISM. 511 



became so in 28 h. ; and that of another still older 

 one, 1J inch in height, remained horizontal during 

 two days, but distinctly circumnutated during this 

 whole time. 



When the cotyledons of Phalaris or Avena are laid 

 horizontally, the uppermost part first bends upwards, 

 and then the lower part ; consequently, after the lower 

 part has become much curved upwards, the upper part 

 is compelled to curve backwards in an opposite direc- 

 tion, in order to straighten itself and to stand ver- 

 tically ; and this subsequent straightening process is 

 likewise due to apogeotropism. The upper part of 

 8 young cotyledons of Phalaris were made rigid by 

 being cemented to thin glass rods, so that this part 

 could not bend in the least ; nevertheless, the basal 

 part was not prevented from curving upward. A stem 

 or other organ which bends upwards through apogeo- 

 tropism exerts considerable force; its own weight, 

 which has of course to be lifted, was sufficient in 

 almost every instance to cause the part at first to bend 

 a little downwards ; but the downward course was 

 often rendered oblique by the simultaneous circum- 

 nutating movement. The cotyledons of Avena placed 

 horizontally, besides lifting their own weight, were 

 able to furrow the soft sand above them, so as to leave 

 little crescentic open spaces on the lower sides of their 

 bases; and this is a remarkable proof of the force 

 exerted. 



As the tips of the cotyledons of Phalaris and Avena 

 bend upwards through the action of apogeotropism 

 before the basal part, and as these same tips when 

 excited by a lateral light transmit some influence to 

 the lower part, causing it to bend, we thought that 

 the same rule might hold good with apogeotropism. 

 Consequently, the tips of 7 cotyledons of Phalaris were 



