RESPIRATION IN THE ROOTS OP SHORE-PLANTS. 329 



The roots that show the greatest resistance to the passage of 

 air, are those of the Fxcfccaria. Tlie habitat of this tree is not 

 in such close proximity to tlie shore as tliat of Avicennia, 

 Rhizophora, or ^Eyiceras. 



The same organ I saw on dried stems of Acanthus ilicifolia, 

 another shore plant. 



Guided by the appearances on the roots of ^Egieeras and 

 Exca'avia, the pores of which are found to extend also higher up 

 among the foliage, the conclusion is forced on uie that these root- 

 pores are only modifications of the organs called lenticels. 



The lenticels of the genei-ality of trees differ somewhat from 

 the root-pore in having no cup-like margins, and the corky mass 

 does not fall freely in the form of powder, as is found in the root 

 of Avicemiia. Yet air can be blown through these organs among 

 the foliage of ^Egiceras, less freely in Excwcaria. With Paquelin's 

 bellows and patience, it may be seen to issue from the lenticels on 

 the young shoots of the peacli, and by the same apparatus can be 

 made to pass through the stomata near the midrib of tlie common 

 Oleander. 80 far, I have seen air issue through the stomata of no 

 other leaf, though experimenting with many. 



Examining all my botanic authorities, I observe no account of 

 the root organs of these plants, and the function of the lenticel is 

 not laid down with certainty. The only botanist, whose writings 

 I have perused, who has given a correct theory for the function 

 of the lenticel, is our esteemed Professor Balfour, who says : 

 *' Lenticels keep up a connection between the air and the inner 

 bark, and probably perform the function of stomata in the 

 advanced period of the growth of the plant." 



One might suppose that in deciduous exogens the lenticels 

 perform important duties before the leaves are unfolded in the 

 spring. 



Turning over Leunis' " Botanic Synopsis," lenticels are there 

 called Korkwarzen and Kinderhoeckerchen, and Mohl believes 

 them to be the first indication of cork formation. No mention is 

 . made of any function in this work. 



Decandolle conjectured they were points developed for the 

 emission of roots. 



The microscopic structure of the lenticel is similar to tlie root- 

 pore of the shore plants, and its functions must be that of 

 respiration. Root-pores then may not inappropriately be called 

 foramina ]mruinatica. 



The microscopic appearance of the foramen of the root of the 

 mangrove being larger than the others mentioned, is worthy of 

 attention. Air passes through it with the greatest freedom. The 

 colour of the corky powder is reddish-brown. The cells are in 

 regular layers which, when observed in siUi from above, shew a 

 honeycomb-like surface. The cells peel off in layers, and when 



