PHYSIOLOGICAL BOTANY. 221 



It is very wrong to repudiate physio-philosophy as 

 paying no regard to facts, but proceeding with purely 

 mental conceptions. Such is not the case. Oken, Nees 

 v. Esenbeck, and Wilbrand, like all other physio-philo- 

 sophers, assume facts as their basis; and only err, in 

 my opinion, in comprising them under ideas of too wide 

 an extent. Thus, under the idea of polarity, they 

 include so many heterogeneous phenomena, that the 

 definition and application of the idea becomes too arbi- 

 trary. In general, polarity signifies an antithesis in 

 different directions. This occurs very frequently in 

 nature, but so generally, that recourse to it not only 

 becomes tiresome, but even superfluous, and withdraws 

 us from more important and exact investigations. More 

 accurate and strict definition of the ideas is requisite, and 

 this again necessitates more minute and rigid determina- 

 tion of the facts. The opponents of physio-philosophy 

 have erred in this respect also. Thus the idea of a cell, 

 as now generally understood, cannot be mistaken ; but 

 when we find how the embryo-sac, the cells of the pith 

 and bark, spiral vessels and the joints of the Algae are 

 so comprised in this term, that what applies to one is 

 considered as holding good as regards the others, there 

 is risk of falling into the most serious errors. The 

 greatest injury effected by physio-philosophy, has arisen 

 from its not only rejecting mechanical philosophy, but 

 even holding it in contempt. Hence the fundamental 

 theories of physics, the theories of motion, have been 

 so neglected in courses of instruction, that we have had 

 to censure the want of acquaintance with them above, 

 even in the opponents of physio-philosophy themselves. 



; INTERNAL STRUCTURE OF PLANTS. 



In no department of physiological botany, if we except 

 the formation of the embryo, has so much been done 

 during the last few years, as on the formation and deve- 



