PATHOLOGIC PLANT ANATOMY 371 



host. The zoospores of the species of Synchytrium penetrate the epi- 

 dermal cells and incite these cells to active growth causing their enlarge- 

 ment, as in the cells attacked by Synchytrium drabcB. Sometimes the 

 infected cell grows inordinately and pushes the mesophyll cells lying 

 below apart, until it projects into the underlying cells as a spheric 

 pouch. If the neighboring epidermal cells are stimulated warts are 

 formed. 



The second group of gall hypertrophies are certain hair-like develop- 

 ments of epidermal cells due to the irritation of certain mites of the 

 genus Phytoptus, which produce felt-galls, or Erineum. These erineum 

 structures arise in clusters on the surface of leaves of such trees as 

 maples, alders, birches, beeches, oaks, willows, limes and on herba- 

 ceous plants belonging to the genera Geranium, Mentha, Salvia, etc. 

 These outgrowths so resemble fungi, that Persoon was deceived into 

 so believing. They are usually pale, or even white at first, and they 

 turn brown as the hair-like outgrowths die and lose their sap, but 

 since the latter may be colored yellow, red or purple, the outgrowths are 

 conspicuous objects on smooth leaves. The botanist Malpighi in 

 1675-1629 was the first to call attention to these galls. One-celled 

 erinea are the rule, but multicellular abnormal hairs are formed by the 

 hypertrophies of the normal trichomes as Frank reports on Quercus 

 (Bgilops. 



Gall hypertrophies, where the ground tissues of plants participate in 

 their formation, are known. The roots of the CYCADACEiE develop 

 sacs out of their parenchyma cells, so that large interceUular spaces are 

 formed in which a blue-green alga, Anaboena cycadearum, the causal 

 organism, lives. Galls produced by flies and belonging to the group of 

 zoocecidia may be taken as illustrations of gall hypertrophies. One is 

 known as the window gall of the maple, and the other is a reddish-brown, 

 bladder gall occurring on the leaves of Viburnum lantanum. 



Multinuclear giant cells may be formed in plants, if the nuclei divide 

 regularly, but for some reason the formation of cross-walls becomes 

 impossible. The cells are stimulated to abnormal growth forming the 

 so-called giant cells. Such hypertrophies are associated with an in- 

 crease of the cytoplasmic contents of the cells. Such giant cells are 

 those produced by certain Nematode worms of the genus Heterodera on 

 such host plants as Beta, Coleus, Daucus, Plantago and Saccharum (Fig. 

 148). Prilleux produced multinuclear giant cells in seedlings which 



