E4 



« 



Size of the cell is demiSnsrirrable , an examination into the 

 size development of cells for phenomena of arrestment will 

 not be, purposeless, 



Imeltmg ascertained that "in the case of parts ©f 

 plants morphologically equal, the medium cell-sizes re- 

 main the same in spite of extraordinary differences in 

 size,-'- The question must still be discussed whether 

 plant organs, dwarfed "by the force of abnormal life con- 

 ditions, lack of water, insufficient nutrition, etc, -are 

 composed of elements of equal size with normal organs. If 

 it was necessary above to emphasize the fact that abnormal- 

 ly small organisms or organs are produced exclusively or 

 predominantly by reduction of the cell number, it should 

 now be added, that reduction of the cell size in all cases 

 which are to be designated as arrested developments, in 

 which, therefore no compensation takes place through in- 

 crease of the cell-number, must lead necessarily to the 

 formation of abnormally small, slender organs. In many 

 oases, moreover, reduction of the cell number is combined 

 with a decrease in cell-volumne. We will therefore have 

 to return repeatedly to the examples given above. 



To be sure, dwarf -forms, at fining only a fifth or a 

 tenth of the normal size, as stated above, do not consist 

 of cells proportionately decreased in site; yet an evident 

 reduction of the vol-urane may be verified, at least in cer- 

 29 tain kinds of cells . It is interesting that many kinds are 

 somewhgt more susceptible than others and many easily re- 

 main below the normal size development, while others, even 

 in highly dwarfed specimens, retain their normal size. Thos^r 

 taiacheal tubes, in which a reduction in diameter may be 

 constantly recognized, belong to the first class. (Compare 

 fig. 6), The epidermal cells of leaf blades generally 

 retain their normal volumne, v;hile the cells of the meso- 

 phyll are greatly reduced,^ 



Influences, other than those which call forth the 

 "dwarfing" of whole plants, also arrest very appreciably 

 the growth of the mesophyll cells. First of all, a com- 

 parison of sun and shade leaves proves this : in the latter 

 not only the mesophyll cells are often greatly shortened, 

 ,but even the epidermal cells may be very small, for in- 

 stance, inXJ^icus stipulata, (compare fig. 8a and b.) The 

 same reduction in cell size may be verified in those var- 

 ieties with pale green leaves, which Griffon (loc . cit.) 



1, Ueber mittlere Zellengrossen. Flora, 1893, Bd. L2pCVII» 

 p. 176, Compare also Schnegg^ Beitr. zur Kenntnis der 6at- 

 tung Gunnera, Ibid., 1902, Bd.- XC, 'g, 161 



E, Compare especially Gauchery, loc. cit. As exceptions 

 are mentioned the dwarf leaves of Polygonum gagopyrum the 

 epidermal cells of which are perceptibly smaller than thosee 

 of normally grown specimens. Compare further H. Moller, 

 loc. cit. Sorauer, Einfluss d. Luftfeuohtlgkeit , Bot-, 

 Zeitg,, 1878, Bd. ZXXVI, p. 1, 



