36 



31 



for a few cases. It is known that newel^'' produced cross 

 wall€ are formed from the system of kinopessmatons. "spindle 

 fibres", which become visible during karyokinesis, or re- 

 main independent of the nuclear division figure. After it 

 has been proved that karyokinesis may be replaced by simpler 

 amitotic stages of cell division, by means of various kinds 

 of e3qperimental interference,' we will have to investigate 

 more closely in what way normal amitotic di-j'ision of the 

 body influences the mode of formation of cross walls. 



In Oedogonium, whose cross wall formation is laiown 

 to be initiated by the deposition of a, cellulose ring, a 

 simplified mode of wall formation without the celluose rina 

 may be observed as the result of abundant sugar nutritionV^ 



CELL GOSfTBNTS 



Of the special contents of the plant cells which come 

 under our consideration, the chromatophor6s and especially 

 the chloroplasts afe the most important, not only on account 

 of their wide distribution in the plant kingdom and their 

 important physiological significance, but also on account 

 of their sensitiveness to various external factors, by 

 which their development is easily and often arrested, 



The development of the chloroplasts can be arrested in 

 many ways,- the number of chlorophyll grains which are un- 

 ited in one cell remains below the normal, or the individtial 

 chlorophyll grains do not attain their normal character, 

 remaining small, or free from chlorophyll, or they end their 

 existence as chlorophyll grains, instead of developing into 

 yellow or red chromatophores. 



The number of chlorophyll grains ■ remains belpw normal 

 in the cells of many variegated leaves, in many varieties 

 with pale green leaves, ^ and in plants cultivated in places 

 T\^ith, atmosphere saturated with vapor* Under the same con- 

 ditions, the size of the individual grains also is often 

 abnormally small. I do not doubt th-at under the influence 

 of certain "arresting" factors, even the form of those" in- 

 dividual chromatophores can undergo a "simplification",' 

 which, as is well known in the gase of many green algae, 

 diatoms and brown and red algae, are remarkable for their 

 complex characteristic organization. 



Those cases demand especial attention in which the 

 formation of the characteristic green coloring matter, the 

 chlorophyll, in the chromatophores, is abnormally omitted. 

 As is well known, the formation of the chlorophyll takes 

 place only within certain temperature limits. It presup- 

 poses, further, with some exceptions, the action of light, 



1, Klebs, Bedingungen der Fortpfl. Bei Algen und 

 Pilzen Jena, 1896, p. 288, 



2, Compare Griffin loc. cit. 



