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. Wakker, 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 





FiQ. 233. — GyTmwsporfingium. sabinae in the form of Roestclia cancellata on 

 leaves of Pear. A few twigs showing the abundance of aecidia over tlie 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 the upper leaf-surface, the palisade parenchyma 



^ Fentzling [loc. cit. ) and Peglion (Eivista di Patologia Vegetak, ii. ), also describe 

 these alterations. 



