128 Rev. P. Keith ow the Conditions of Life. 



Both have an alimentary and a sexual apparatus; for both 

 grow and propagate their kind. Both have an apparatus for 

 tlie propulsion and distribution of fluids, which they have the 

 capacity of assimilating to their own substance. — But animals 

 have additional faculties, and the additional faculties in ques- 

 tion have their source in additional organs; while the organs 

 conferred correspond to the wants of the individual. The food 

 of the plant is already digested ; but the animal has its food to 

 digest. Hence the necessity of a stomach. The plant is sta- 

 tionary ; but the animal moves. Hence the necessity of a 

 muscular apparatus. The plant is insentient; but the animal 

 is endowed with the faculty of sensation. Hence the cerebral 

 system, the source of thought, perception, consciousness, me- 

 mory, volition, loco-motion. In the lower orders of animals 

 these additional properties are not very distinctly marked ; but 

 as you ascend the scale, they become more and more visible 

 till at last you reach man, in whom they exist in the highest 

 degree. 



Aeration. — No living being can thrive, or even continue to 

 exist, without the access and contact of atmospheric air. 

 The seeds of vegetables will not germinate if placed in vacuo. 

 Ray introduced some grains of lettuce-seed into the receiver 

 of an air-pump, which he then exhausted : they did not ger-. 

 minate, but they germinated upon the re- admission of the air; 

 which shows that access of air is a condition necessary to the 

 germination of seeds*. The experiments of Homberg seem 

 indeed to militate somewhat against this conclusion. They 

 are recorded in the Memoirs of the French Academy for the 

 year 1669; and the inference deduced from them is, that seeds 

 in general do not germinate if deprived of atmospheric air; 

 but that cress-seed, lettuce-seed and a few others will germi- 

 nate even in the vacuum of an air-pump. But the same ex- 

 periments when repeated afterwards by Boyle, Muschenbroek, 

 and Boerhaave, with a much better apparatus, did not confirm 

 the latter part of the result. On the contrary they all tended 

 to prove that no seed germinates in the vacuum of an air- 

 pump, and that in the cases of germination mentioned by 

 Homberg, the vacuum must have been very imperfect. The 

 same experiments were again repeated by Saussure the younger, 

 who says that the seeds of peas gave indications of germination 

 ill vacuo in the course of four days, but never effected any de- 

 velopment of parts beyond the mere protrusion of the radiclef . 

 — We conclude, then, upon the whole, that in a perfect vacuum 

 no seed will germinate ; but that in the most perfect vacuum 

 hitherto formed by human art, some seeds may germinate. 



* Phil. Trans. No. xiii. f Sanssurc siir la Fig. chap i, sect. 1. 



The 



