Evolution of Structure in Seedlings. 47 



cylinders were loosely closed below by a cork, and filled to 

 within half an inch of the top with fine earth or vegetable 

 mould. They were then placed erect in a covered tin box or 

 tube-stand, in such a manner that the lower end dipped into 

 water contained in the box, while the whole of the cylinder 

 except the top was kept in the dark. Thus the first condition 

 for germination, viz. darkness, was secured; the second, warmth, 

 was supplied by the external temperature, which varied from 

 70° to 80° F. ; while regularity and uniformity in the supply of 

 moisture in both series was secured by having a box of cylin- 

 ders or tubes for each and keeping the level of the water the 

 same in both. The supply of oxygen was also equal and 

 uniform, since the upper part of each tube presented a similar 

 opening to the air. 



Thus prepared, one box, containing five cylinders, was kept 

 in a dark closet, while a second, similar in all respects, was 

 pjaced in a window of tl;e adjoining room, where it was ex- 

 posed to direct sunlight five or six hours every day. To each 

 tube a light wooden rod thirty inches in length was attached ; 

 and on this the growth of the seedling was marked every 

 twelve hours. The hours selected were 7 a.m. and 7 p.m. I 

 thus obtained the night and day, or dark and light growth of 

 every seedling, as long as those in the dark grew. The seeds 

 were planted on June 1st, and appeared above the ground on 

 June 6th, when the measurements were commenced. In each 

 series one seed failed to germinate ; the record consequently is 

 for four plants in each. The history of the evolution of 

 structures is as follows : — 



Evolution of structure in the dark. — In Table I. the seeds are 

 designated as A, B, C, D ; and each column shows the dates on 

 which leaves and lateral growths appeared. These constitute 

 periods in the development of the plants, which are indicated 

 by the numbers 1, 2, 3, 4, 5, 6. The weight of each seed is 

 given in milligrammes. 



Table I. — Seedlings grown in the dark. 



A. B. C. D. 



Weight of seed.... 431. 436. 456. 500. 



Period 1 7th day. 7th day. 7th day. 7th day. 



„ 2 8th „ 9th „ 9th „ 8th „ 



„ 3 10th „ 10th „ 11th „ 10th „ 



„ 4 12th „ 12th „ 13th „ 12th „ 



„ 5 14th „ 15th „ 15th „ 14th „ 



„ 6 17th „ 18th „ 18th „ 17th „ 



A glance at the above shows the uniformity as regards 



