588 Estological Investigations on Intumescences, ete. 
generally, oxygen are the necessary external factors. But the more recent 
investigations bring out the importance of certain internal or biological 
factors, namely, writabiity and either actwe powers of assimilation or 
abundance of stored food material. 
(5) Finally, the nuclear phenomena were investigated and compared, and 
were found to be in every respect identical in various intumescences and in 
wound-callus. Pathological tissues in certain plants and animals are also 
compared, and a strong resemblance is seen to exist between certain rapidly 
formed outgrowths in plants and animals, caused not by any parasitic 
organism, but simply by the influence of some stimulus, probably always 
external, acting upon a plant or animal in such a condition of irritability 
that it is able to respond. A similar resemblance occurs between regenera- 
tive wound tissues in certain plants and animals, the formation of which 
is in all cases accompanied exclusively by the more rapid form of nuclear 
division known as amitotic or direct. 
