Chapter VI —53— The Plastlds 



of chlorophyll. Still others think they are lipides holding the pig- 

 ment in solution (Menke, Weber). 



With the study of this structure the question of the double re- 

 fraction of chloroplasts has been brought up again. While KtJSTER 

 concludes that double refraction is due to the ground substance of 

 the chloroplast, Menke, Heitz, and Weber attribute it to the 

 grana which, accordingly, they believe correspond to doubly refrac- 

 tive lipide inclusions. Menke and Weber observed that after a 

 prolonged stay in water, the chloroplasts are the seat of the pro- 

 duction of green myelin filaments which correspond to the fibrils 

 of SCHWARZ and which arise from the grana^ Now WEBER 

 showed that these myelin figures when seen in polarized light pre- 

 sent the same double refraction and same red color as do the grana, 

 which he thinks tends to prove that in the chloroplasts only the 

 grana are doubly refractive and that these elements correspond 

 to liquid cristals^. 



It is known, however, that GiROUD had recorded that the chon- 

 driosomes of animal cells, which we will see later on are akin to 

 plastids, appear doubly refractive. Weber to confirm his opinion 

 examined chondriosomes and leucoplasts of various plants in polar- 

 ized light but was not able with certainty to prove that they are 

 doubly refractive. It is known, of course, that carotin in chromo- 

 plasts, when it is not crystallized, appears as clearly separated 

 granules in the colorless substance of the plastid. Now in examin- 

 ing such chromoplasts in polarized light, Weber was able to demon- 

 strate that the double refraction is localized exclusively at the 

 level of the pigment granules. This seems to demonstrate that the 

 substratum of the plastids is not doubly refractive and that this 

 characteristic is due to the grana in chromoplasts and chloroplasts 

 alike. The problem of the structure of the chloroplasts is certainly 

 very complicated, since it is difficult to avoid alterations in living 

 material during observation, but the tendencies are manifestly in 

 favor of a heterogeneous structure. Most authors (Heitz, Doutre- 

 LiGNE, WiELER, Deschendorfer, Weber, Pekarek, Geitler) agree 

 that the chloroplasts are composed of small lipide discs containing 

 chlorophyll and embedded in a hydrophilic stroma. Weber thinks 

 these discs are responsible for the fiuorescence of chlorophyll and 

 the double refraction of the chloroplasts. 



Recently Frey-Wyssling has attributed a lamellate submicro- 

 scopic structure to these discs, consisting of a series of parallel 

 layers of protein, lecithin, chlorophyll and carotinoid pigment. 

 The scheme of this author implies that the phytol groups of the 

 chlorophyll molecules are interposed between aliphatic chains of the 

 lecithins, the porphin residues being arranged in a monomolecular 



'By placing Spirogyra in a 1-2% solution of sodium oleate, Weber saw the spiral bands 

 of the chloroplast swell and form protuberances on their surfaces reminiscent of myelin 

 figures and sphaerocrystals. These formations are green like the chloroplasts and correspond 

 to the lipide phase of the chloroplast. 



^Webeb thinks these grana may correspond to the granules considered by Meyer to be 

 formed of crP hexylene-aldehyde, a product of photosynthesis, which we will speak of again 

 farther on. 



