CHAP, iv.] Origin of Tissues. 317 



pure historic ground ; for the majority of the men who have 

 developed modern doctrines since 1840 are still alive, and it 

 must be uncertain whether the account here attempted may 

 not be impugned on some ground or other. Owing to the 

 extraordinary diversity of opinion that exists among botanists 

 even on the most general questions in the science, it is 

 extremely difficult to ascertain what can be considered as 

 a common possession, an unfortunate condition of things, 

 from which no science perhaps suffers so much as botany. 



The extent to which individual botanists have contributed 

 to the advance of phytotomy during the period under consider- 

 ation will appear of itself from the following narrative ; and 

 if we speak almost exclusively of Germans, it is for the simple 

 reason that Englishmen from Crew's time till now can scarcely 

 be said to have added anything to our knowledge of phyto- 

 tomy ; the Italians also, once so gloriously represented by 

 Malpighi, scarcely come under consideration in the questions 

 now to be dealt with, while^ French botanists, represented 

 by Mirbel in the preceding period, though they have produced 

 many works on phytotomy since his time, have had no impor- 

 tant share in deciding the fundamental questions of modern 

 science. 



In the preceding period it was necessary to take into 

 consideration the increasing improvement of the microscope, 

 in order to understand the development of opinion on 

 vegetable structure ; but it is scarcely needful to do so after 

 1840. Since that time good and serviceable instruments with 

 strong magnifying powers and clear definition have been 

 within the reach of every phytotomist ; and though improve- 

 ments are still being constantly made, yet the microscopes that 

 were in the hands of skilful observers between 1840 and 1860 

 were fully adequate to deciding the new questions proposed to 

 them. The chief improvement effected in the microscope 

 during this period was the fitting it with apparatus for the 

 polarisation of light, and for the more convenient measurement 



