36 VEGETABLE ORGANOGRAPHY. 



able to discover them. Others consider the claters of 

 the Hepaticae as organs similar to tracheae ; but I cannot 

 admit that there is any real analogy between tracheae 

 and these organs, resembling each other, it is true, in 

 their spiral turnings, but very different in their size, 

 texture, and position. I persist, then, in believing that 

 tnicheag are entirely absent from cellular plants. 



Amongst those which we are obliged to refer to the 

 class of vascular plants, tracheae are wanting, according 

 to Link, in Lemna, Zostera, Ceratophyllum, and 

 Najas, all of them aquatic. Amici confirms their 

 absence in Najas minor, but he is contradicted on this 

 point by Pollini ; and the absence of tracheae in vas- 

 cular plants is a fact which requires to be confirmed, 

 especially since tracheae not capable of being unrolled 

 have been mentioned, and since there have been found 

 true tracheae in Hippuris and Myriopltyllum, where it 

 was at first believed that none existed. 



Several anatomists, and in particular Wahlenberg, 

 Rudolphi, &c., assure us that they have not found 

 tracheae in the Coniferae, neither around the pith, in the 

 leaves, in the younger branches, nor at the first deve- 

 lopment of the plant : this was found to be the case, 

 according to them, in the anatomy of several species of 

 Pines, Deals, Larch, Cedars, Thuja, and Cypress ; but 

 it was already known that true tracheje exist in the 

 young branches of the Juniper, &c. An anomalv so 

 remarkable in the same family was difficult to be 

 admitted : since then, Kieser, in a special treatise 

 on the Coniferae, has shown the existence of them, 

 though they are more rare and more difficult to be seen 

 than in other plants. 



Oken thinks that tracheae are analogous to the 

 nerves of animals. This paradoxical opinion has not, 

 that I am aware of, been admitted by any naturalist : it 



