Guilliermond - Atkinson 



— 48 



Cytoplasm 



with eccentric hilum, on the contrary, arises at a point near the 

 periphery of the plastid and, in this case, by enlarging, soon pro- 

 jects beyond the plastid, which no longer covers it except at one of 

 its poles where it takes the form of a cap. The hilum surrounded 

 by the earliest formed layers is then found at the extremity of the 

 grain opposite the plastidial cap. The grain, no longer coming 

 under the influence of the plastid in that region, ceases to grow 

 and enlargement no longer takes place except at the point of con- 

 tact with the plastid, i.e., at the pole opposite the hilum. There 

 the concentric layers become increasingly numerous and thick. 

 The compound grain arises by a plastid forming several starch 

 grains inside itself, instead of only one. These are in contact with 

 one another and remain small. They are semi-compound grains 

 if they become surrounded by common concentric layers. 



On the basis of all his investi- 

 gations, as well as those of 

 SCHMITZ on the algae, Schimper 

 was led to consider the plastids 

 as component parts of the cell, 

 incapable of arising de novo, be- 

 ing transmitted by division from 

 cell to cell beginning with the 

 egg, so that plastids of higher 

 plants, according to him, are com- 

 parable to the chloroplasts which 

 are encountered permanently in 

 many algae, but with this differ- 

 ence : in the algae the plastids al- 

 ways keep their chlorophyll and 

 remain as green plastids, while in 

 higher plants they appear first as 

 leucoplasts and do not become 

 chloroplasts except in stem and 



leaf tissue. 



Arthur Meyer (1883) working at the same time, confirmed 

 the theory of Schimper which was verified also as far as the 

 chromoplasts are concerned by Courchet (1888). 



It is fitting to call attention to the observation that the plas- 

 tids, at the same time that they are elaborating starch and pig- 

 ments, are capable of producing inside themselves small re- 

 fracting granules which reduce osmic acid (Fig. 18). To these, 

 which are sometimes very numerous, a lipide constitution has been 

 attributed. These granules were described long ago by Nageli, 

 Godlewski, Schimper, Meyer. They have been the object of 

 more recent research by Meyer who has opposed the idea of their 

 lipide nature and considers them to be composed of a-(3 hexylene- 

 aldehyde, a waste product of photosynthetic assimilation found in 

 the products of the distillation of the leaves. Meyer calls these 

 formations elaborated by the plastids Autoplastensekret. We shall 

 see, nevertheless, that this interpretation has not been confirmed 



,^£5^==^ 



F^G. 17. — Various aspects of chromo- 

 plasts derived from chloroplasts in the meso- 

 carp of the fruit of Rosa canina (in vivo) . 



