316 Development of the Cell and [Book ii. 



The researches of Hofmeister, N'ageli, Hanstein, Sanio, and 

 others into the first formation of vascular bundles from the 

 fundamental tissue of young organs led to important results 

 for morphology, in so far as it was now for the first time 

 possible to judge of the morphological value of anatomical 

 and histological relations. The growth in thickness of woody 

 plants, a question of primary importance to vegetable physi- 

 ology, was first made intelligible by the discovery of the mode 

 of formation of vascular bundles and their true relation to 

 cambium ; Hanstein and Nageli, and afterwards Sanio espe- 

 cially, cleared up the questions connected with growth in 

 thickness in their main features before and after i860. 



When we pass on to show how the great results above- 

 mentioned were attained, we encounter some difficulties. 

 After 1840 botanical literature multiplied to an extent before 

 unknown ; it is from elaborate monographs on single subjects 

 in phytotomy, from some text-books, and especially from smaller 

 essays in botanical periodicals that we must gather an account 

 of the further development of scientific thought. Much as the 

 founding of scientific periodicals has facilitated communication 

 between professed botanists, yet this form of literature makes 

 it more difficult to see the way clearly through the work of 

 earlier periods and to discover the historical connection in the 

 science, not to speak of the harm that usually results from it to 

 young and inexperienced students. 



Such being the nature of the sources from which we must 

 draw our information, we shall obtain a better general view of 

 the whole subject if we depart from the practice of former 

 chapters, and follow out the more important questions in their 

 historical development instead of connecting them directly 

 with leading persons. Such a treatment of the subject is 

 indeed suggested by the fact that we are now no longer on 



