Guilliermond - Atkinson — 50 — Cytoplasm 



leucoplasts in living cells and asserted that starch arises most 

 often within the cytoplasm itself and that chloroplasts form by 

 cytoplasmic differentiation. The development of the plastids was 

 very imperfectly known and even the most characteristic forms 

 which the plastids take on were not known. Progress in this 

 matter was not marked until much later, from 1910 on, when re- 

 search was carried out with so-called mitochondrial technique 

 which makes possible the preservation of unaltered plastids, clearly 

 stained on paraffin sections. This will be taken up later. These 

 methods have made it possible to follow with the greatest precision 

 the entire life history of the plastids during cellular development ; 

 to bring out different aspects which up to then had not been per- 

 ceived; and to make important discoveries which have confirmed 

 the ideas of Schimper and Meyer by completing them and giving 

 them precision. 



Chemical nature and structure of plastids :- 



Plastids for a long time were thought to be ex- 

 clusively protein in nature. It was however be- 

 lieved, without anyone being able to furnish proof 

 for it, that plastids must enclose a lipide sub- 

 stance, probably lecithin, in which the chlorophyll 

 was supposed to be dissolved. Gautier, Hoppe- 

 Seyler and Stoklasa even formulated the hy- 

 pothesis that chlorophyll is a chlorolecithin. The 

 presence of lipides in chloroplasts is not ques- 

 tioned today and Menke, chiefly, seems to have 

 piS ilf 'aTaSIcS- furnished a proof of it. Granick, by triturating 

 matous cell of Echi- g^^d then ccutrifuging tobacco and tomato leaves, 



noeereita procumbens iij-ij j^- i.-j_ j?ii„ 



showing large inciu- was able to isolate a certam quantity oi chloro- 

 ^}^^^ °KJ?^^^'if^''°^' plasts and to obtain their microchemical analysis. 



/ Affpjt Miss Manu- 



EL). Granick thus managed to separate proteins from 



lipides. Recent work, which will be discussed 

 later, has shown by histochemical reactions that in reality all plas- 

 tids, like the cytoplasm, are composed of lipoproteins in which, 

 however, the lipides (compound lipides, probably lecithins) are 

 much richer than in the cytoplasm and give to the plastids their 

 color characteristics. 



The importance of the plastids in photosynthetic assimilation 

 has led authors for a long time to attribute a structure to these 

 organelles. The leucoplasts appear homogeneous and the chloro- 

 plasts, and chromoplasts especially, have been studied from this 

 point of view. 



Let us recall that these organelles are formed of a lipoprotein 

 substratum on which the chlorophyll is fixed (chlorophyll a and 

 b), accompanied by a small quantity of carotinoid pigments (caro- 

 tin and xanthophyll). 



Pringsheim, Tschirch, and Chodat held that the chloroplasts 

 consist of a spongy material impregnated with a fluid substance of 

 an oily consistency (lipochlorine of Pringsheim) serving as a sub- 



