124 DECOMPOSITION OF THE SYCAMORE. 



liar to the laurel and the holly. (See Plate 4, 

 Fig. 2.) 



The leaf of the elm in autumn may commonly 

 be observed marked with dark-coloured blotches, 

 which are the " plague spot" of its destruction. 

 These leaves remain in large proportions uninjured 

 through the winter months ; but when spring ar- 

 rives the spots become matured, the surface cracks, 

 and the capsules discharge their seeds. (See Plate 

 4, Fig. 1.) Lamarck names it sphasria xylomoides, 

 but mentions another as a more early observer. At 

 these spots the decay of the leaf generally com- 

 mences. 



Most persons must have observed that the upper 

 surface of the leaves of the sycamore (acer pseu- 

 doplatanus) is blotched with dark-coloured spots 

 (xyloma acerinum) in autumn. This leaf is de- 

 tached by the earliest frosts, and falling to the 

 ground, the spots commence their operations by 

 corroding away the portions of the leaf that sur- 

 rounds them, but continue attached themselves, 

 appearing as raised, shining, vermicular lines. This 

 has been mentioned by Lamarck and others, and is 

 only now noticed to point out the variously consti- 

 tuted agents that accomplish the destruction of the 

 foliage of plants. 



the vessels not containing the capsules in cells, hut loose. Hoff- 

 man observes, that both sphseria and uredo discharge pollen from 

 an orifice ; but, if the summit of this plant be cut off, the capsules 

 are obvious. 



