28 THE PALM-STEM. 



That these vessels, though not the result of a meta- 

 morphosis of spiral vessels, belong to one and the same 

 system, is evident from the fact, that spiral vessels occur 

 in many Monocotyledons in the situation where the reti- 

 cular vessels lie in the Palms, and in the Grasses, as 

 Moldenhawer showed, the same row of tubes is developed 

 at certain places into spiral, and at others into porous 

 vessels. 



The smaller vessels lying behind the reticulated are never 

 reticulated, but always spiral or annular vessels, be the 

 stem under examination as old as it may. The number 

 of annular vessels in each vascular bundle is but small, 

 in general only spiral vessels exist. When annular ves- 

 sels do occur, they are always situated the farthest back in 

 the bundle, the vessels lying nearer to the large vessels 

 being always spiral. The turns of the spiral are always 

 far apart, especially in those vessels which are farthest from 

 the large vessels. It is easy to satisfy one's self of the 

 presence of an outer membrane inclosing the spiral fibre. 



I have mentioned above, under the name of proper 

 vessels (vasa propria), a bundle of thin-walled cells lying 

 between the wood and liber, as the third constituent of 

 the vascular bundle. This bundle is distinguishable from 

 the surrounding cells, both by the thinner walls of its 

 elementary organs, and by narrow and wide cells lying 

 intermingled in it. This part opposes considerable diffi- 

 culty to anatomical investigation, on account of its soft 

 texture, and also its great transparency. This circum- 

 stance explains why these proper vessels, although they 

 occur in most of the Monocotyledons and in a portion of 

 the Dicotyledons, have been overlooked by almost all 

 phytotomists, for Moldenhawer is almost the only one 

 who was accurately acquainted with them, in Zea Mays 

 and Bambusa, while Amici saw them in Calamus, but did 

 not recognise their nature, and Kieser, who likewise saw 

 them in Calamus, explained them as spiral vessels ; 

 Bernhardi and Meyen, the latter of whom found these 

 proper vessels in Scirpus lacuslris and some other Mono- 



