66 INTRODUCTION TO CYTOLOGY 



Elaioplasts. — Special plastids concerned in the elaboration of oil are 

 known in a number of angiosperms'' (Fig. 29). Kiister and Harper have 

 shown in the case of Ornithogalum that the plastid can be recognized 

 before oil appears in it, and that the abundant oil which is present later 

 may be extruded on its surface when the tissue is prepared for observa- 

 tion. Woycicki has observed the fusion of small elaioplasts containing 

 fat droplets to form a large "oleosome" with a central fat drop. In old 

 cells the oleosomes degenerate. Since oil may also occur as droplets 

 directly in the cytoplasm, Harper suggests that much of the current 

 difference of opinion regarding elaioplasts may be due to 

 the fact that among these bodies there may be transitional 

 forms between oily ergastic accumulations not causing 

 any cytoplasmic differentiation and definite cytoplasmic 

 organs in which the production of the oil is localized. 

 Some reported "elaioplasts" seem to be only groups of 

 disorganizing plastids with their products. 

 Eiaioplast " with '^^® Eyespot. — The so-called eyespot, or stigma, present 

 oil droplets in in the flagellates and in the zoospores and gametes of many 

 perianttTof'poZ?- ^^S* ^^^ Certain characteristics in common with plastids 

 anthes tuberosa; and may therefore receive consideration here. This body, 

 small pL^stids at which nearly all workers agree is a light-sensitive organ, 

 right. {After is an elongated or circular and flattened structure lying 

 in the anterior region of the cell (flagellates) or near its 

 lateral margin, usually in close association with the chromatophore and 

 the plasma membrane^ (Fig. 30). With respect to its mode of origin, it 

 has been variously reported to arise de novo in each newly formed zoospore 

 in several green algse (Overton), to multiply by fission at the time of cell- 

 division in flagellates (Klebs), to disperse as granules which reassemble in 

 the daughter cells in Euglena (Jahn), to develop from a plastid in the 

 antheridial cell in the case of the spermatozoid of Fucus,^ and to arise as a 

 differentiated portion of the plastid in the zoospores and gametes of 

 Zanardinia (Yamanouchi). 



It is thought that the eyespot in many instances consists of a finely 

 reticulate stroma in which an oily red pigment with many of the charac- 

 teristics of hsematochrome is held in the form of minute droplets or gran- 

 ules.^ The stroma may also bear one or more refractive inclusions, which 

 in the Chlamydomonadaceae and Volvocace* consist of starch and in the 

 Euglenoideae of paramylum. These inclusions were thought by Franze to 



« Wakker (1888), A. Zimmermann (1893), Raciborski (1893), Kuster (1894), Beer 

 (1909a), Politis (1914a), Guilliermond (19226), Harper (1929), W6ycicki (19296). 



7 E. Overton (1889), Klebs (1883, 1892), L. N. Johnson (1893), Strasburger (1900a). 

 WoUenweber (1907, 1908), Hall and Jahn (1929). 



sQuignard (1889), Mangenot (1920e, 1921), Kylin (1920). 



8 Schilling (1891), Klebs (1883), Franze (1893), Wager (1900a), WoUenweber 

 (1907, 1908). 



