666 Wisconsin Academy of SciencesArts, and Letters. 
Pringsheim concluded that the proteid of the chlorophyl 
grain consists of a spongy reticulum, which he called the 
“stroma.” This stroma is saturated with a green solution con¬ 
sisting of an oil, in which the cholorophyl is dissolved. Prings- 
heim’s. results have been supported by those of Schmitz and 
Meyer, who were of the opinion that the stroma consists, not 
of a homogeneous plasmatic body, but of a porous, spongy 
mass. Meyer has also found dark-colored grains imbedded in 
the stroma, which he calls “grana.” Schimper concluded that 
the chloroplasts consist of a colorless stroma containing nu¬ 
merous vacuoles filled with the green chlorophyl in solution. 
ISTageli, in 1846 (23, p. 143), was the first to observe the 
leucoplasts. He described them as vesicles filled with starch. 
Schimper, in 1880 (35, p. 881), described the leucoplasts as 
specialized colorless organs of the cytoplasm which he called 
“starch formers.” In a later paper he gave them the name 
“leucoplasts.” According to Schimper, the earliest mention 
of chromoplasts is by linger in 1846. Yon Mohl (20, p. 361), 
in 1851, mentions the yellow crescent-shaped color bodies 
found in the yellow leaves of Strelitzia. Schimper (34, p. 
2), in 1885, found evidence that they are homologous with the 
chloroplasts and may arise from the same rudiments in the 
e gg< 
The leucoplast has been termed by many physiologists a cell 
organ. We also consider a plant cell from one of the higher 
plants as a unit of structure of an organ of the plant. The 
higher plants are made up of tissues and organs, and from this 
standpoint the cell is the unit which cannot be sub-divided 
into units comparable to cells. But the cell is also an organ¬ 
ism, and we may properly speak of those parts of the cell which 
have a permanent existence and perform a special function 
as cell organs. These are not homologous, however, with the 
organs of the higher plants, nor is the organization of the cell 
directly comparable to that of a plant part. From this stand¬ 
point we may call plastids and vacuoles cell organs. Verworn 
(41, p. 58) has proposed to call them “organoids,” but there 
seems to be slight justification for calling them organ-like 
bodies when they belong to a morphologically different class. 
