250 



It must still be noted that definite processes, kttownin 

 normal development, can take place with abnormal intensity, 

 more v;eakly or iiore strongly than under normal conditions, and 

 further that different parts of the cell can undergo an unequal 

 formation, when the determinative conditions can not h©oom« 

 effective ■r.n the same way in all parts pf the cell. 



Undev normal conditions, plants, possessing the ability 

 to form scXereids, can produce unusually thln-walled or very 

 thick-vailled solereide; or, stead of cells distended equally " 

 on all sides, one-sided ones may be produced etc. To be sure, 

 V9 know nothing of the causes of the stimulation her© effective. 

 But the galls speak in favor of our hypethesis,- at tiraBS the 

 Cynipides gall of Querous, in v,'hich we found developed very 

 different kinds of sclereids* The fact has been discussed 

 above in detail (p* 241) that certain kinds of unequally thick- 

 ened solereids 8S well as many other histological oharacteristicB 

 furnish attributes constant for the separate gall forms, 



Only an apparent exception to the rule here developed 

 Is made by the irregular, sometim&s elliptical or spherical, r 

 sometimes cone or ooral-llke wall -thickenings, which are 

 often ferraed by the action of external distiiroances butare 

 absolutely lacking In normal cells of the plant spMles con- 

 cerned. I have already referred (Chapter III) to the fact 

 that these thickenings have fto definite form and no charac- 

 teristic structure In so far that aXl pitting la lacking 

 In them* I would therefore like to assume that this kind * 

 of waXl-thickenlng so far as its ultimate form Is concerned, 

 is not dependent on definite capabilities of the cytoplasm, 

 Rather, its special qualities seem to have as little te do 

 with the form of the thickenings as they have possibly tdth 

 the form of the precipitates produced in the cell by the 

 action of external factors. The formation of membrane accum- 

 ulations, coralloid cones, etc. does not in my opinion make 

 necessary the assutoptlon that newly ooonrring qualities of 

 the cytoplasm lie gt the base of their formation. 



On account of the peculiar thickening of their cell 

 walls; (compare p. 211) the threads foxind in the gall of 

 Ustllago Treub ii. which resemble capillitia, are very no- 

 ticeable . SKriilustration given out by Salms-Iiaubaoh 

 throws no exact light on the nature of these thickenings 

 nor of their production. Doubtless, we will be concerned 

 in their formp.tion only with processes, of which the normal 

 cells are also capable. 



As long as it is not possible to cause a turning green of 

 the cells of plants whitfi are free from chlorophyll, of the de- 

 velopment of traoheids in the tissue of cell cryptogames so 

 (292) long as stone cells or wood-fibres are not found in the abnorm&l 

 tissues of p].ants which are free from sclereids or stereids, - 

 we mav hold to the assumption that in the formation of cells 

 under" abnormal cor.ditions, only the "normal" capacities, of the 

 cells will come ii-itc question and x^w qualities will «ever 

 arise. Should anyone evef be so fortunate as to call forth 

 new qualities experimentally, he will thereby solve a phylogen- 

 etic question and produce a new species. 



So far as ±t known at present, the varying structures of 

 abnormal tissues are produced by combinations of processes of 

 growth and forme.tion, other than those made under normal condi- 

 tions. Just as a "piano by virtue of its construction is 



