54 



CIRCUMNUTATION OF SEEDLINGS. CHAP. L 



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'gth 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 

 rflmd several seedlings which had risen through very fine 

 argillaceous sand, kept uniformly damp. 



Zea mays (Gramineje). 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 cotyledon > 

 travelled all daylong to this side, though making in their course 

 Borne conspicuous flexures, from wnich fact alone we might have 



