I. CONTENT t)F THE CELL 5'6 



The formation of chlorophyl l in cells, which normally remali: 

 free from* chlorophyll , is one of the most frequent ancL most strik- 

 ine metaplastic changes. The action of light, which, as is we^-1- 

 known, is indispensihle for most pSants in the formation of chlor- 

 ophyll, often calls forth a metaplastic greening in organs whieh 

 under normal conditions would have been kept from the light; 

 tubers, bulbs, rhizomes and roots of F/^ny plants, as eIso the cot- 

 yledons of many seedlings, commonly germinating :*n the soil, be- 

 come green in light. According to the prevailing theory of the 

 production of chloroplasts we must assume that the colorless chro- 

 matophores (leucoplasts) present in the cells of underground or- 

 gans are transformed under the influence of light into carrier- s 

 of green coloring matter* In this connection it is worthy of note 

 that in all underground organs only a moderate degree of green- 

 coloration is obtainable when they become green metaplastically. 

 Their shade differs widely from the color of typical assimilatcry 

 organs, and resembles rather the pale green of many lower or e'de 

 leaves or the coleoptila of some grasses. Cotyledons of Vioia 

 and others, removed from the stem of the seedling, become gre6n- 

 relatively strongly when left in the light. It must be observed 

 further that not all colorless cells and organs become green 

 through the action of light; while the roots of Cucarbita, Menyan- 

 thes,Zea and many others may then become a pale green; the roots 

 of other plants remain perm&nently colorless, pollen tubes are or- 

 gans on chlorophyll-bearing plants which have never been changed 

 to green, and they remain colorless even under the prolonged in- , 

 fluenoe of light and cultivation under the most varied conditions . 

 In these and similar cases, we must for the present leave unset- 

 tled the question, whether this occurs only because the "right" 

 combination of conditions has not yet been found which would make 

 possible the turning green of these organs, or whether they have 

 lost the ability to form chlorophyll, i. e, , the possession of 

 leucoplasts capable of development. 



Bonnier"^ found thst the tissue of his experimental plants, 

 which were uninterruptedly exposed to the light of arc-lamps, 

 turned green even to the pith,- the cells of the medullary rays 

 and of the medulla, normally colorless, contained chlorophyll. 

 But whether the appearance of the chloroplasts may be considered 

 as an effect of the continuous expotiure to ligjit is not demon- 

 strated with certainty by Bonnier 's investigatflons. 



Without doubt other action thajs that of light can induce also 

 a metaplastic greening. The formation of chlorophyll in hyper- 

 trophied epidermal cells, which will be considered later, favors 

 this as well as the "turning green'^ of corollas, anthers and ovules 

 from the action of parasites, the treatment of which belongs to 

 the province of pathological ^norpholog-y^. 



Ittore exact proof is still needed as to how far an increase 

 of chlorophy^.! grains can be incited by the action of chemicals, 



^~The old statements of- Reissek (Bot, Zeitg., 1844, Bd, II, 

 p. 505) are based ^ of course, on a confusion of the pollen sacs 

 with thread-like algae. 



^ Infl» de la lumiere electrique continue a. la forme et la 

 forme d/ pi. Rev, gen, Bot., 1895, T, VII, p. E41. 



^ The statements of 0. Ktaiis. (Ueb. kunstl. Chlorophyller- ^ 

 zeugung in leb. Pfl. bei Lichtausschluss. Landwirtsch. Versuchssta 

 1877, Bd. ZX. p. 415), according tc which etiolated plants can b3 

 incited to the formation of chlorophyll by methyl alcohol or by 

 mechanical arrestment of their growth in length, need testing. 



