122 
Sydney H. Vises. 
covered with a tubulaled bell-jar closed by a cork (Fig. 2). From the 
cork a watch-glass was suspended by means of a wire, and it was pos- 
sible to introduce, ihrough a Perforation in the cork which could be 
opened or closed at pleasure, a small quantity of baryta-water into the 
watch-glass, to serve as a lest of the absence or presence of carbonic acid 
in the air. 
From a great number of experiments pcrformed in this way I select 
the following as an example. 
June 2 2. A joung plant of Cucurbita pepo (1) was placed over 
potash as above described, and a similar plant (2) was placed under a 
bell-jar over water. Both were removed and measured on June 29. (coty- 
ledons) 
June 22 
June 29 
length 
breadth 
lengtli 
breadth 
No. t 
3.15 cm 
1.9 cm 
4.4 cm 
2.5 cm 
No. 2 
3.0 cm 
1.8 cm 
4.8 cm 
2.5 cm 
No. 1 : contained starch in guard-cells of stomala, and in sheath cells 
of fibro-vascular bundles only. 
No. 2: the cells of the spongy parenchyma contained numerous 
starch grains. 
This experiment affords dislinct evidence of the growth of the coly- 
ledons in the absence of assimilation. The only possible source of error 
is that the air may not have been absolutely free from carbonic acid. 
By means of the baryta-water test I found that during the night a suf- 
ficient quantity of C0 2 generally remained unabsorbed by the potash to 
cause a slight cloudiness in the baryta-water by the following morning, 
bul the total precipitate of barium carbonate produced after an exposure 
of two or three days w'ithin the bell-jar was less than that produced by 
an exposure of a few minules to ordinary air. Il is evident that the 
amount of carbonic acid left unabsorbed was quite inadequate to provide 
the amount of carbon necessarj for the amount of organic substance which 
would correspond to the growth which took place. 
In order to avoid this source of error I made another series of expe- 
rimenls with the apparatus shewn in Fig. 3. It consists of a slout wooden 
stand, with a thick metal rod, E, upon which four supporling rings can 
slide. Upon the lower pair of these rings two small perforated saucers, 
similar to the one previously described, are supported (i d' d "). Through 
the aperture of each of these saucers the cotylcdons of a seedling are 
passed, and the stem is fastened by means of a split cork and some 
soft wax, the roots of the plant-remaining in the pot below the saucer. 
