254 Report S.A.A. Advancement of Science. 



from the nearest plants, and made to slant outwards from them till 

 the shadow just left their roots at 8h. 43m. Those which were 6 

 inches further off in Row I. had their roots in shadow till 8h. 6m. 

 The leaves of all the plants were in sunlight about 18 minutes 

 previously. 



By March 26th six of the 7 peas belonging to Row L were in 

 flower, but only one of the 7 in Row II. On the 27th the pea in 

 Row I, which had not flowered (No. 10) had begun to turn yellow. 

 Its tendrils had no coil in them, and especially those highest up the 

 stem, were hanging limp. By the 28th the condition of the plant 

 was so bad that it was feared that it would die. No. 11 next to it 

 was also turning yellow, especially on the south side, which received 

 the sunlight 2 to 3 minutes later than on the north side. Its tendrils 

 also had lost their coil. Both 10 and 11 were measurably smaller in 

 every way than those next them, both in the dimensions of their stems 

 and of their leaves. None of the other peas behind the screen were 

 as yellow as 10 and 11, but all were distinctly smaller than those at 

 the south end of the rows, which received rays as early as 6h. 45m. 

 As it was important that 10 and 11 should not die, in which case 

 the decay might have been attributed to bad seed, insects, or to soil, 

 the screen was lowered before sunrise on the 29th, so as to allow 

 them to be in full sunlight a little earlier. This was effected 

 by sloping the screen outwards without otherwise altering its 

 position. It is suggested that the change of colour was not an effect 

 of temperature, but of distribution of the chlorophyll-granules on 

 the walls of the cells under the action of light. This view is 

 supported by the fact that No. 11 continued to turn yellow all 

 through the 29th and 30th. The prejudicial action was not arrested 

 suddenly. 



The alteration of the screen allowed direct sunlight to fall on 

 both 10 and 11 about three-quarters of an hour earlier, and as soon 

 as the first ray touched the roots of 10 at 7h. 25m. on the 31st, the 

 tendrils began to coil for the first time. The plant remained stunted 

 and yellow, but from this onwards the chlorophyll began to return 

 to the foliage, and there was never any doubt but that the plant would 

 survive. Similarly No. 11 had become green and healthy by March 

 31st. It had received direct rays 4 minutes before No. 10 each 

 morning. On March 30th there were stratus clouds at sunrise, and at 

 2 p.m. a heavy shower of rain fell, accompanied by some thunder. 



So far, these experiments were in favour of the hypothesis that 

 cutting off the early rays till after 8h. was prejudicial to such plants 

 as peas, onions, lettuces, and beets ; and that not only was the growth 

 affected by variations in temperature, but that the _ chlorophyll- 

 granules were being disadvantageously arranged for doing work, by 

 the intense illumination they were subjected to during the day. It 

 appeared as if the early rays were required to distribute the granules 

 to the best advantage, and enable them to recover from the effects 

 of the intense sunlight of the previous day. 



