PICTURESQUE EXPERIMENTS 215 



pressers in London I proceeded to visit one of them 

 somewhere in Hoxton. He turned out to be of a 

 highly suspicious disposition, but his wife had more 

 discernment, and persuaded him that I was a 

 harmless customer, with no designs on trade 

 secrets, and I finally obtained what I wanted. A 

 dehcate strip of horn was fixed to a httle block of 

 cork and placed on a leaf, and to my delight showed 

 the stomata to be open by violently curving up- 

 wards. It was only necessary to fix a graduated 

 arc to the cork, and to fasten ai delicate hair on to 

 the horn so as to serve as index. The instrument 

 is not of course accurately quantitative, but it 

 does at least show whether the stomata are nearly 

 shut, moderately open, or widely so; Rough as it 

 is I found it good enough for determining a number 

 of interesting facts in the physiology of stomata.^ 

 I now pass on to a different subject, the all- 

 important process on which the life of green plants 

 depends, an act therefore by which our own exist- 

 ence and that of all other animals is conditioned. 

 I mean the process known as assimilation. This 

 is the truly miraculous feat of using as a source of 

 food the carbonic acid gas (C.Oj) which exists in 

 minute quantities in the atmosphere. The plant 

 is in fact a carbon-catching machine, and the 

 machine is driven by the energy of the sun, and can 

 therefore only work in light. The eminent Russian 

 botanist, TimiriazefF, in a lecture on this subject^ 

 before the Royal Society, made a witty use of 

 Gulliver's Travels — a book not commonly quoted 



'^ Phil. Trans., B. vol 190, 1898. * See above, p. 136. 



