THE FERN TRIBE. 5267 



the designation of cellular plants, because their 

 stems rarely contain vessels, but usually consist of 

 cellular substance only. You, perhaps, do not know 

 that, in nearly all plants which bear flowers, there 

 are present those curious air-pipes, called spiral ves- 

 sels, of which I long ago gave you an explanation 

 (p. 38.) ; such, however, is the fact. On the other 

 hand, in these flowerless plants, spiral vessels are uni- 

 versally absent ; some of the most highly organized 

 tribes, such as those which form the subject of the 

 present letter, have a particular kind of vessel in lieu 

 of the spiral ; but all the other tribes are destitute of 

 vessels of any kind. 



Ferns, which are the most completely organised of 

 Flowerless plants, and which approach nearer than 

 any others to the Flowering tribes, are those to which 

 I would first call your attention. In the northern 

 parts of the world, they are green leafy productions, 

 which die down to the ground every year ; and they 

 are seldom more than two or three feet high ; one of 

 the larger kinds is the Brake (Pteris), which is so much 

 esteemed as covert for game. But, in tropical coun- 

 tries, many of them far surpass these pigmy dimen- 

 sions ; they acquire real trunks, resembling those 

 of Palms, and often rise to as high as forty or fifty 

 feet without a leaf; even a more considerable sta- 

 ture is spoken of by travellers. At all times they 

 are graceful objects, from the slender wiry stems 

 on which they bear their leaves, which wave in 

 the breeze like plumes of feathers, and from the 

 multitude of leaflets into which they are cut with 



