18 



The diversity manifested in the arrestment of cell and 

 of tisgiae development is very similar. Either the nrimher 

 of the cells composing a certain organ or forming a"^certain 

 definite tissue, remain helow the normal, or the size of the 

 individual cells is smaller than under normal condi ti ons , or 

 finally, the internal structure of the cells and the differ-^ 

 entiation of the tissues stops at g, priraitave stage. Hence 

 the succeeding elaborations follow v;ithout further discussion. 



Arrested developments of the most varied kinds are to be 

 observed abundantly, on the one hand, in many :,jlants in nat- 

 ure, or on the other hand, may be readily called forth by 

 experimental interference at any time. Since, furthermore, 

 arrested development of cells and tissues is often combined^ 

 with Some obvious external characteristics, the attention of 

 the botanist has been repeatedly directed to them. Corres- 

 pondingly, a surprisingly large number of reports may be 

 found in the literature bearing upon the same abnormal con- 

 ditions. On account of the often very inadequate content 

 of the works, it will be sufficient to mention only selected 

 ones in the discussion which follows, 



A. mJMBSR OF CELLS. 



We have spoken already of arrested developments, in 

 which the bulk of whole organisms or sing'le organs remained 

 beJ.ov; the normal -^-roportions. In so-called Nanism, that is, 

 TzStfen the plants attain only a fifth or a ten*^. of their normal 

 size as a result of continued drought or unfavorable nutri- 

 tion, a corresponding reduction of the size of the cells 

 to a fifth or a tenth of their normal proportions does not 

 take place parallel to the reduction of the. plant volume; 

 on the contrary, the cells of the dwarf spe.cjmens consist 

 (E3) essentially of cells approximately as large as those of 

 ■ normal individuals; the small size of the starved indivi- 

 duals being Chiefly brought about by a reduction in the 

 number of cells,-'- 



Similar conditions exist if only single organs, leaves, 

 blossoms, fruits, and not entire plants are dwarfed. For our 

 histological consideration, however, in both cases, only these 

 come into question in which decrease in the number of cells in 

 connection with a shortening of the internodes, a reduction 

 of the leaf-blade, etc. brings about a variation in the his- 

 tology of the organs Concerned. Such cases exist, for ex- 

 ample, if the number of the cell layers in the mesophyll de- 

 creases, if, by the disappearance of one or more palisade lay- 

 ers, the proportion between palisade and spongy parenchyma 



1, Compare for instance, Holier, H., Beitr. zur Kenntnis 

 der Verzwergung fUanismus) . Landv/irtschaftl. Jahrb,, 1884, 

 Bd. XIII, p. 167 and especially Gauchery, Rec. sur le nanisme 

 vegetal, Ann. Soc. Mat* Bot. , YIII, serie, T, IX, 1899, 

 p, 61. (Further literature is quoted therein.) 



