398 



UREDINEAE. 



The anatomical changes exhibited in diseased parts of pear- 

 leaves have been briefly described by Fentzling/ He found a 

 radial elongation of the. cells of the spongy parenchyma and an 

 accompanying accumulation of starch. AVakker, about the same 

 time, obtained similar results in the case of Crataegus Oxyacantha 

 deformed by G. clavariaeforme (see p. 387). Wakker observed 

 a diminished formation of calcium oxalate ; Fentzling, however, 

 found increased deposit of the same salt, not only in the form of 



Fio. 233. — Gi/mnosporangiaiii sahitiac in the form of liotstcUa. canccllata on 

 leaves of Pear. A few twigs showing the abundance of aecidia over the whole 

 tree. (v. Tubeuf phot.) 



isolated crystals but as masses. Cork-formation was suspended 

 in Wakker's case, while in Fentzling's a partial formation of 

 cork was distinguishable beneath the epidermis. The increased 

 thickness of diseased leaves- is due principally to multiplication 

 of the spongy parenchyma, the upper layers of which frequently 

 become more or less palisade-like. When pycnidia (spermogonia) 

 are formed on tlic upper leaf-surface, the palisade parenchyma 



^ Fentzling (lor. cit. ) and Peglion (Rivista di Patologia Vegetale, ii. ), also describe 

 these alterations. 



