230 
W. C. TWISS 
Sachs, in his Text-book of Botany, in 1882, where the process is compared 
to that of so-called free-cell formation. Since the work of Schimper, 
afterwards confirmed by that of A. Meyer, the opinion has become general 
that the three kinds of plastids found in plant cells, namely, leuco-, chloro-, 
and chromoplasts, are derived from minute, undifferentiated plastids which 
are sui generis structures of the cytoplasm. These chromatophores, as 
they are often called, were described, when seen in the living cell, as small, 
colorless, highly refractive bodies, recognizable in the egg and also in the 
embryonic cells. In older cells they have been said to retain the same 
appearance in some cases, while in others they become differentiated into 
leuco-, chloro-, and chromoplasts. 
Schimper and Meyer believed that the undifferentiated plastids multiply 
by division and are handed dow^n from generation to generation — that they 
have an individual existence in the cells. Considerable difficulty, however, 
was encountered by them in their attempts to demonstrate the presence of 
the plastids in the egg, owing to the fact that they were not easily seen in 
the living cells, and, as was admitted, they were difficult to stain at that 
stage. As Guilliermond expresses it, ''that part of their theory remained 
very hypothetical." 
When the mitochondria were demonstrated, by means of a special 
technique, their study was first taken up by the zoologists, as has been shown, 
and special functions in the cell metabolism were imputed to them by 
Meves and others. Pensa is credited with having made the first observa- 
tions tending to show that the mitochondria of plants may, possibly, be 
transformed plastids. This idea, developed by Lewitsky and Pensa and 
supported by numerous observations which have already been noted, was 
taken up by Guilliermond, who has attempted particularly to harmonize 
the functions of the mi ochondria of plant cells with the theories concerning 
those of the mitochondria of animal cells as postulated by Meves, Dues- 
berg, Regaud, Dubreuil, and others. He has confirmed the observations 
of Lewitsky and of Pensa by work upon a number of plants, including the 
seedling of barley. Here the mitochondria, followed from the meristem 
toward the green tip of the plumule, are shown as filamentous at first, 
followed by shorter and thicker forms which are sometimes dumb-bell 
shaped. From the appearance in succeeding cells of bodies which have the 
appearance of the separated halves of the "dumb-bells," he believes that 
the latter divide. These bodies are followed by more rounded forms with 
a light center and a darker border. Finally, in the tip of the plumule, the 
mature chloroplasts are seen. While this series is considered by Guillier- 
mond a very convincing proof of the mitochondrial origin of the chloroplasts, 
it is open to the objection that there seems to be no way of demonstrating 
that the Anlagen of the plastids are actually mitochondria and not merely 
young plastids. 
On the other hand, the attempts of Rudolph, Sapehin, Mottier, and 
J 
