220 The Anatomy of Plants BOOK n 



perhaps transitory, may cause different changes in different 

 plants or in the same plant at different ages, or under different 

 conditions. The structure, looked at from that standpoint, 

 may disclose a good deal about the conditions of the past 

 life of the race or of the individual, but it is not likely 

 to illustrate, still less to explain, questions of phylogeny 

 and affinity. The latter questions deal with fundamental, 

 the former with fluctuating problems, and the greater im- 

 portance of relationship must be admitted. 



The separate contributions made by authors to the 

 general subject of anatomy were far too numerous even for 

 mention here. The study was so general and so widespread, 

 that communications of greater or less importance were 

 of almost daily occurrence. We cannot, therefore, do more 

 than briefly allude to the more prominent lines of work. 



The structure of the vessels of the wood and the nature 

 of the pitting which characterizes them, were the subjects 

 of research by Caspary in 1862. He attempted to trace 

 the connexion between the true vessel and the tracheid, 

 but his conclusions were not sound. He denied the exis- 

 tence of vessels altogether in the Pteridophyta and in 

 many Phanerogams. Dippel was more successful in 1865 ,' 

 in his memoir he showed how gradual is the passage from 

 one form to the other. His account of pitting was not 

 quite so satisfactory, as he considered the bordered pits to 

 have no pit-closing membrane, a point on which he was 

 at issue with the discoveries of Hartig some years earlier, 

 and with Schacht's work of 1859. The question was finally 

 settled by the researches of Sachs in 1879 and of Mikosch 

 in 1881, in which the development of the bordered pit was 

 traced. Strasburger confirmed this work in his Bau und 

 Wachstum of 1882. 



Schenk contributed a valuable research on lianes in 1883. 



The occurrence of internal phloem in the central cylinder 

 of certain natural orders was demonstrated by Vesque in 1875. 



