Chap. L SOLANUM. 51 



Solarium paUnacanthum. — Several arched hypocotyls rising 

 nearly '2 of an inch, above the ground, but with the cotyledons 

 still buried beneath the surface, were obserred, and the tracings 

 showed that they ciroumnutated. Moreover, in several cases 

 little open circular spaces or cracks in the argillaceous sand 

 which surrounded the arched hypocotyls were visible, and 

 these appeared to have been made by the hypocotyls having 

 bent first to one and then to another side whilst growing up- 

 wards. In two instances the vertical arches were observed to 

 move to a considerable distance backwards from the point where 

 the cotyledons lay buried; this movement, which has been 

 noticed in some other cases, and which seems to aid in extracting 

 Ihe cotyledons from the buried seed-coats, is due to the com- 

 mencement of the straightening of the hypocotyl. In order to 

 prevent this latter movement, the two legs of an arch, the 



Fig. 38. 



Solarium palinncant''Um : circumnntation of an arched hypocotyl, jtist 

 emerging from the ground, with the two legs tied together, traced iu 

 darkness on a horizontal glass, from 9,20 A.M. Dec. 17th to 8.30 A.M. 

 19th. Movement of bead magnified 13 times; but the filament, which 

 was affixed obli4Ucly to the crown of the arch, was of unusual length. 



summit of which was on a level with the surface of the soil, 

 were tied together ; the earth having been previously removed 

 to a little depth all round. The movement of the arch during 

 47 hours under these unnatural circumstances is exhibited 

 in the annexed figure. 



The cotyledons of some seedlings in the hot-house were hori- 

 zontal about noon on December 13th ; and at 10 p.m. had risen 

 to an angle of 27° above the horizon ; at 7 a.m. on the following 



