CIRCUMNUTATION OF SEEDLINGS. CHAP. I. 



scope with a micrometer eye -piece, so arranged that each 

 division equalled ^^th of an inch. After an interval of 30. m. 

 the apex was observed, and it was seen to cross a little obliquely 

 two divisions of the micrometer in 9 m. 15 s. ; and after a few 

 minutes it crossed the same space in 8 m. 50 s. The seedling 

 was again observed after an intervalof three-quarters of an hour, 

 and now the apex crossed rather obliquely two divisions in 10 m. 

 We may therefore conclude that it was travelling at about the 

 rate of -g^th of an inch in 45 minutes. We may also conclude 

 from these and the previous observations, that the seedlings of 

 Phalaris in breaking through the surface of the soil circum- 

 nutate as much as the surrounding pressure will permit. This 

 fact accounts (as in the case before given of the asparagus) for 

 a circular, narrow, open space or crack being distinctly visible 

 round several seedlings which had risen through very fine 

 argillaceous sand, kept uniformly damp. 



Zea mays (Grammes). A glass filament was fixed obliquely 



to the summit of a cotyledon, 

 rising -2 of an inch above the 

 ground ; but by the third morn- 

 ing it had grown to exactly 

 thrice this height, so that the 

 distance of the bead from the 

 mark below was greatly in- 

 creased, consequently the trac- 

 ing (Fig. 51) was much more 

 magnified on the first than on 

 the second day. The upper 

 part of the cotyledon changed 

 ^_ > - its course by at least as much 



Fig. 51. 



Zea mays : circumnutation of cotyle- 

 don, traced on horizontal glass, from 

 8.30 A.M. Feb. 4th to 8 A.M. 6th. 

 Movement of bead magnified on an 

 average about 25 times. 



as a rectangle six times on each 

 of the two days. The plant 

 was illuminated by an obscure 

 light from vertically above. 

 This was a necessary precau- 

 tion, as on the previous day we had traced the movements of 

 cotyledons placed in a deep box, the inner side of which was 

 feebly illuminated on one side from a distant north-east window, 

 and at each observation by a wax taper held for a minute or 

 two on the same side ; and the result was that the cotyledons 

 travelled all day long to this side, though making in their course 

 some conspicuous flexures, from which fact alone we might have 



