i88 9 .J 



BOTANICAL GAZETTK. 



39 







Moeller as having an internal periderm, or what is the same, 

 producing a bark. What the connection is, or whether the 

 knovvledge of the exact structure of the internal would throw 

 any light on the function of the superficial periderm 1 am 

 not able to sa}^. 



In Euonymus alatus we have not the puzzling feature of 

 eccentric growth, but the question of utility and the reason 

 tor such an outlay of material arises with still greater force. 

 Here the last suggestion in reference to the wing of Liquidam- 

 bar may be applied. In all the species of this genus it is an 

 evident fact that the stem performs, in part, the office of 

 assimilation. i his is especially marked in the case of E. 

 alatus, the chlorophyll-holding cells even having the form 

 and arrangement of the regular palisade cells of leaves, 

 while the number and size of leaves indicate the need of the 

 aid of the stem in performing this labor. Now in sterns even 

 with the most exaggerated wings, both as to width and depth, 

 it is still very evident that the entire surface, which acted as 

 assimilating tissue before the beginning of the wings, still 

 retains its original character and sustains the same relation 

 to the outside air as before, during at least the first two 

 years' growth of stem. By referring to the figures the com- 

 paratively immense gain in surface by the wing development 

 is seen, while the surface, with the original palisade c lis, 

 remains intact and in working order. Now. were the ma- 

 terial in these wings evenly distributed around the stem early 

 enough to allow its growth in diameter, all assimilation of 

 the stem would be effectually checked. By the present ar- 

 rangement, the protection of a partial superficial periderm 

 is given to the stem, assimilation is not checked, exchange 01 

 gases goes on by means of the stomata and whatever there 

 may be taking place through the young tissue of the wing 

 lying in lines along near the surface. It will be remembered 



that these walls are never suberized. The anatomy of E. 



Europaeus and its varieties indicates a similar function. Sur- 

 face growth is increased here with less outlay of material 

 than in E. alatus, the wings never acquiring such size in the 

 direction perpendicular to the surface. 



The development of cork tissue from its beginning, was 

 studied only in the two forms given, E. alatus and E. Euro- 

 pa?us, var. purpurea ; in these the origin of the pliello- n 

 cells was not the same, those of the first occurring about the 

 stomata, and of the second in the thick-walled collenchy- 

 matic cells of the corner. Therefore it is not safe to draw 



