THE PARASITIC EXOASCEAE. 157 



Exoascus communis Sad. This produces pocket-plums on 

 Prunus americana, P. pumila, and P. maritima in America. 



Similar " pockets " also occur on Prunus suhcordata, P. Chicasa, 

 and P. pennsylvanica, in America, as a result of some Eocoascus. 



Exoascus Farlowii Sad. produces similar 

 deformation of carpels and floral envelopes on 

 Prunios serotina in North America. 



Exoascus Johansonii Sad. produces carpel- 

 enlargement on the female catkins of Populus 

 iremula, P. tremuloides and P. grandidentata ; the 

 contents of the asci are yellow. (Fig. 52.) The 

 anatomy of the deformed ovaries has just been 

 described by Sadebeck.^ 



Exoascus rhizophorus Johan. causes similar Fm. 52.-Exoascus 



p-r»T Johansonii Sad. on 



enlargement of the female catkms of Populus Popuiustranuia. (v. 



° -^ TubeufdeL) 



■alba. 



Exoascus alni-incanae Kiihn (Hx. amentorum Sad.) This 

 species is readily distinguished by the absence of a stalk-cell 

 on the ascus. It causes increased growth and enlargement 

 of the seed-scales of alder catkins, the fruit itself being seldom 

 attacked. The fleshy bladder-like outgrowths at first appear 

 as little red processes ; later, the asci are developed on the 

 outer surface as a whitish coating. On many of these red 

 processes may stiU be recognized the trifid apex of the normal 

 scale, (this is really formed from five smaller scales fused into 

 a single large one with a trifid apex). A number of these 

 red outgrowths are generally present on each infected catkin, 

 yet the alders continue to flower vigorously every year. 



Wakker,^ in investigating the anatomy of the deformed scales, 

 found the following alterations : — the scales are increased to many 

 times their original size and contain two cavities; all parenchy- 

 matous cells become regular and iso-diametric ; lignification of 

 the elements of the wood is more or less interfered with, and 

 fewer wood-fibres are produced ; there is an accumulation of 

 transitory starch. 



Exoascus alni-glutinosae Tubeuf. This is a new species 



distinguished by v. Tubeuf in 1895. It occurs in the Sudetic 



mountains, Italy, Denmark, and Sweden, on Alnus glutinosa. 



Its habit is similar to that of Ex. alni-incanae, but the asci 



' Sadebeck (See Literature), 4. p. 144. ^ Pringsheim's Jahrbuch, 1892. 



