NAEGELI 115 



Von Mohl had gone astray. He also elucidated the 

 structure of sieve tubes which had been identified by 

 Hartig in 1851. He formulated a classification of tissues, 

 distinguishing them into generative and permanent, 

 both being again subdivided into parenchymatous and 

 prosenchymatous types. The primary parenchymatous 

 generating tissue occurred, according to Naegeli, in all 

 embryos and young organs, while the prosenchymatous 

 meristem, which he called " cambium/' was arranged in 

 strands or layers in fully developed organs and between 

 permanent tissues. The permanent tissues thus took 

 their origin either in primary or secondary meristem. 

 Accepting Hanstein's views as to leaf trace bundles, he 

 further distinguished regions in the bundles as foliar, 

 common, and cauline. 



Even from this brief summary of the researches of 

 these two men you will appreciate how much plant 

 anatomy owes to them ; but their labours were not 

 confined to microscopic investigations, for we shall find 

 their names cropping up again and again during the next 

 decade or two in connection with other developments of 

 the science. Meanwhile you will observe that histology 

 has begun to wear a more familiar aspect, and to resemble 

 in many respects the accounts met with in present-day 

 treatises on the subject. There are still many details to 

 be filled in, but the foundations are securely laid. 



