370 GENERAL PLANT PATHOLOGY 



Tyloses^ are more or less closely packed, bladder-shaped intrusions 

 derived from the parenchyma cells adjoining the cavities of water- 

 conducting elements into which they project, often completely blocking 

 the cavities (Fig. 146). They were first investigated by Hermine von 

 Reichenbach, who noticed that the swelling is not cut ofiF from the 

 parent cell by a septum. They arise frequently in association with one- 

 sided bordered pits, the limiting membranes of which undergo active 

 surface growth and thus push their way into the cavities of the vessels 

 (Fig. 147). Several tyloses may arise from a single epidermal cell. They 

 occur beneath branch scars that have been formed by a branch breaking 

 off and also at the wounded end of cuttings being formed in such 

 numbers, that they become flattened by mutual pressure. The cavities 

 of vessels are thus filled and they probably serve, as Boehm first sug- 

 gested, to plug up the cavities of the water-conducting tubes that have 

 suffered mechanic injury. This explanation suffices for such special 

 cases of injury, but tyloses are formed in uninjured vessels where they 

 obviously do not serve to close up a wound. Haberlandt believes that 

 tyloses of this last-mentioned type take some part in the process of 

 conduction, by increasing the surface of contact between the vessels 

 and the neighboring parenchyma cells. Kiister in his "Pathological 

 Plant Anatomy" gives a detailed account of the different kinds of 

 tyloses and their method of formation, which need hardly be discussed 

 in a text-book for student use. Molisch gives a list of plants in which 

 tyloses have been found. Sometimes tyloses fill the air chambers of 

 the stomata partially or almost entirely, where the epidermal cells 

 adjacent to the guard cells grow out into large unicellular bags, as in 

 Tradescantia viridis. 



Gall hypertrophies are those which are produced by the effect of a 

 poison formed by an attacking animal, or plant. The tissue products 

 are the most diverse and a sharp distinction cannot be drawn between 

 hypertrophic and hyperplastic gall tissues. Gall hypertrophies usually 

 occur in the epidermal and the fundamental tissues of various plants. 

 The galls of the fungi belonging to the family Chytridiace^, namely, 

 those occasioned by species of Synchytrium, are very simple, for the 

 entire life history of the fungous parasite is passed in a single cell of the 



1 Gerry, Eloise: Tyloses: Their Occurrence and Practical Significance in Some 

 American Woods. Journal of Agricultural Research, i: 445-470, with 8 plates, 

 March 25, 1914. 



