PL AST IDS AND CHONDRIOSOMES 111 



Quite different were the views of Gargeanne (1903). According to 

 him they arise from vacuoles, their limiting membranes thus being the 

 original tonoplasts. While in the juvenile vacuole stage they may multi- 

 ply by division, but when once fully formed they remain unchanged and 

 divide no further. Gargeanne observed small oil droplets moving about 

 freely within the oil body, and hence concluded that the latter has a 

 fluid consistency rather than a spongy stroma as Kiister thought. 



The most noteworthy recent observations on oil bodies are those of 

 Rivett (1918), who finds them to be very conspicuous in the cells of 

 Alicularia scolaris. Rivett holds that they are in reality only oil vacuoles 

 that they originate by the coalescence of numerous minute oil droplets 

 secreted by the protoplasm in a manner entirely similar to that in which 

 the ordinary sap vacuole arises (cf. Pfeffer). Although they become very 

 large and project well into the sap vacuole, they continue to be surrounded 

 by a thin film of cytoplasm. The oil body, in the opinion of Rivett, is 

 therefore in no sense a plastid, nor is it formed by any special elaioplast : 

 it is simply an accumulation of ethereal and fatty oils together with some 

 protein substance. The "membrane" observed by Pfeffer is the limiting 

 layer of the surrounding cytoplasm, which may be slightly changed by 

 contact with the oil. 



Accumulations of oil apparently quite similar to those in liverwort 

 cells have been described in the cells of various angiosperms by a number 

 of writers. To these the term elaiospheres was applied by Lidforss (1893). 



The published figures of elaioplasts and oil bodies in many cases 

 bear striking resemblance to those of fat- and oil-secreting chondrio- 

 somes (see below), and it is not improbable that the problem of their 

 origin and significance will be brought nearer solution by further studies 

 of the latter class of bodies. 



The Eyespot. The so-called eyespot present in the flagellate cell and 

 in the zoospores and gametes of many algae has certain characteristics 

 in common with plastids, and may therefore receive consideration here. 

 This body, which nearly all workers agree is a light-sensitive organ, 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 associa- 

 tion with the chromatophore and the plasma membrane. (Overtoil 

 1889; Klebs 1883, 1892; Johnson 1893; Strasburger 1900; Wollenweber 

 1907, 1908). With respect to its mode of origin, it has been variously 

 reported to arise de novo in each newly formed zoospore in several green 

 algae (Overton); to develop from a colorless plastid in the young 

 antheridial cell in the case of the spermatozoid of Fucus (Guignard 1889) ; 

 to arise as a differentiated portion of the plastid in the zoospores and 

 gametes of Zanardinia ( Yamanouchi) ; and finally to multiply by fission 

 at the time of cell-division in flagellates (Klebs 1892). 



It is generally agreed that the eyespot in many instances consists of 



