t28 MODIFIED CIECUMNUTATION. Chap. Vin 



for the first 45 m. in a zigzag line; it then felt the full influence 

 of the light, and travelled towards it for the next 2 h. 30 m. in an 

 almost straight line. The tracing has not been given, as it was 

 almost identical with that of Apios under similar circum- 

 stances (Fig. 170). By noon it had bowed itself to its full 

 extent ; it then circumnutated about the same spot and described 

 two ellipses ; by 5 p.m. it had retreated considerably from the 

 light, through the action of apogeotropism. After some pre- 

 liminary trials for ascertaining the right degree of obscurity, 

 some seedlings were placed (Sept. 16th) before a north-east 

 window, and light was admitted through an ordinary linen 

 and three muslin blinds. A pencil held close by the pot now 

 cast a very faint shadow on a white card, pointing from the 

 window. In the evening, at 4.30, and again at 6 p.m., some of 

 the blinds were removed. In Fig. 174 we see the course pursued 

 under these circumstances by a rather old and not very sensitive 

 cotyledon, 1"9 inch in height, which became much bowed, 

 but was never rectangularly bent towards the light. From 

 11 A.M., when the sky became rather duller, until 6.30 p.m., the 

 zigzagging was conspicuous, and evidently consisted of drawn- 

 out ellipses. After 6.30 p.m. and during the night, it retreated 

 in a crooked line from the window. Another and younger seed- 

 ling moved during the same time much more quickly and to a 

 much greater distance, in an only slightly zigzag line towards 

 the light ; by 11 a.m. it was bent almost rectangularly in this 

 direction, and now circumnutated about the same place. 



Tropceolum majus. — Some very young fee llings, bearing only 

 two leaves, and therefore not as yet arrived at the climbing 

 stage of growth, were first tried before a north-east window 

 without any blind. The epicotyls bowed themselves towards 

 the light so rapidly that in little more than 3 h. their tips 

 pointed rectangularly towards it. The lines traced were either 

 nearly straight or slightly zigzag ; and in this latter case we 

 see that a trace of circumnutation was retained even under the 

 influence of a moderately bright light. Twice whilst these 

 epicotyls were bending towards the window, dots were made 

 every 5 or 6 minutes, in order to detect any trace of lateral 

 movement, but there was hardly any ; and the lines formed by 

 their j auction were nearly straight, or only very slightly zigzag, 

 as in the other pxrts of the f.gures. After the epicotyls had 

 bowed themselves to the full extent towards the light, ellipses 

 of considerable size were described in the usual manner. 



