PHYTOGENY. 223 



tracheae also terminate in the circumference of the 

 node. 



1119. The formation of nodes consequently ranks 

 directly under the stelliform formation of branches. 

 Taken in a strict sense the formation of nodes occurs 

 only in plants with sheathing leaves or in Monocoty- 

 ledons. 



3. AIR-ORGAN, FOLIAGE. 



1120. If in the progressive separation of the tissues 

 the tracheas finally obtain the preponderance, so that 

 they issue forth free from the envelope of cellular tissue, 

 the leaves, or Foliage, then originate. 



1121. The ribs of the leaf are the fascicles of trachea 

 that have become free, and are still only connected toge- 

 ther laterally by a thin layer of cellular tissue. 



1122. The leaves can be regarded as gigantic and 

 unrolled spiral vessels, and these again as microscopic 

 and involuted leaves. 



1123. As through the root the water-process enters 

 the plant, and through the stalk the earth-process, so 

 does the air-process through the leaves. 



1124. It is probably the stomata through which the 

 air is conducted into the tracheae ; the connexion, how- 

 ever, has not yet been proved. 



GemmcB or Suds. 



1125. With the formation of branches there is at the 

 same time a diminution of the cellular tissue, and an 

 increase of the tracheae. Entirely new spiral vessels 

 commence in the branches, and are not continued or 

 prolonged into the stalk. The further indeed the ex- 

 tent of the ramification, by so much less is the quantity 

 of cellular tissue, and by so much greater the number of 

 the tracheae. It comes at last to this, that the tracheal 

 fascicles, which were from all sides surrounded by dense 

 cellular tissue, are only then loosely connected by a thin 

 layer of such substance. This ramuscule is still therefore 

 only a hollow stalk, consisting of fascicles of tracheae dis- 



