Carbon Dioxide in Maturation, etc., of Seeds. 417 



germiuation at any time after ripening. The case of the inhibited seeds of 

 Brassica alba offers an exact parallel to this case also. 



(d) Experiments Reproducing in Nature, with C0 2 Naturally Produced, the 

 Results obtained in the Laboratory with Brassica alba Seeds. — In drawing the 

 foregoing parallels, a reflection which is suggested is that the inhibition of 

 the Brassica alba seeds has been produced in the laboratory under conditions 

 remote from those found in nature. 



The following series of experiments were therefore directed to ascertain 

 whether this objection is valid. The outcome of these experiments, it will 

 be seen, is to indicate that the results of inhibition under the influence of 

 CO2 obtained in the laboratory with Brassica alba can be readily reproduced 

 in the soil in conditions such as may occur widely in nature. The method of 

 procedure was as follows: — Pits of various depths were dug in a garden soil 

 consisting of sandy loam with very few stones. Short, fresh-cut grass was 

 spread at the bottom in some cases. In others, green garden rubbish took 

 the place of grass. The earth was then returned to the pits, and seeds, 

 enclosed in small cotton-net bags, were inserted in it at various depths. The 

 CO2 content of the atmosphere of this soil at various depths was taken 

 constantly during the experiments. 



The following was a typical experiment: — On August 16, 1912, a pit 

 18 inches deep and 2 feet square was dug, a layer of packed green grass 

 about 3 inches deep inserted, and the pit then filled up by the return of 

 the earth removed. Seven days later, on August 23, three lots of 25 seeds 

 each were buried at depths of 3, 6, and 9 inches in the earth in this pit 

 over the grass. At the same time three control lots of seeds were placed 

 at corresponding depths in a control pit close by, out of which the earth had 

 been dug, and similarly returned seven days previously, but in which no grass 

 had been placed. 



The following are examples of the percentages of C0 2 found in samples of 

 soil air taken during the experiment at depths of 6 and 12 inches in the pit 

 containing grass : — 



Per cent. Per cent. 



August 23 at depth of 6 inches 12-4 C0 2 ; at depth of 12 inches 18-8 C0 2 . 

 „ 29 „ „ 16-5 C0 2 ; „ „ 20-0 C0 2 . 



In the earth in the control pit, without grass, the C0 2 content of the soil 

 continued steadily at about 1 per cent, at depth of 12 inches. 



After seven days in the soil the seeds were removed and examined. None 

 of those over the pit containing decaying grass had germinated at depths 

 of 6 and 9 inches, while at a depth of 3 inches only 3 out of the 25 seeds 

 had sprouted. All the seeds of the control lots at each depth in the pit 



