164 
to a rise in temperature during the process 
of germination, and his works on fossil 
plants are too extensive and well known to 
require special consideration at this time ; 
but in the prosecution of his studies, he 
strongly emphasized the necessity of treat- 
ing all such remains from a strictly botan- 
ical point of view, and he was ‘especially 
prominent in giving great weight to char- 
acters derived from a study of the internal 
structure, thus recognizing the school al- 
ready founded by Witham in England. 
Corda was already well known for his 
valuable work on the fungi and mosses, 
before entering upon those paleobotanical 
studies through which hisname more com- 
monly appears. 
The great number and value of Unger’s 
contributions to botanical science lent 
special weight to his conclusions respecting 
fossil plants. In 1837 he described the 
spermatoids in various mosses and declared 
them to be the male elements of fertiliza- 
tion. In 1855 he first directed attention 
to the great resemblance between the pro- 
toplasm .of the plant cell and the sarcode 
of the more simple animals,—a discovery 
which was later brought into great promi- 
nence and finally led to the conclusion that 
protoplasm is the foundation of all organic 
development. He was the first to success- 
fully oppose Schleiden’s theory of free cell 
formation as applied to the growing apex 
of stems, and to show that such cells arise 
by division—having their origin in a meri- 
stem. His work, in conjunction with that 
of von Mohl, Nageli, Braun and Hof- 
meister, laid the foundation for a true con- 
ception of cell formation. In his ‘ Anatomie 
und Physiologie der Pflanzen’ he intro- 
duced many new and valuable ideas re- 
specting the character of the protoplasm, 
and gave a concise idea of the cell in its 
various complexes as families, tissues and 
fusions. With von Mohl’s text-book, this 
work accomplished more than any other in 
SCIENCE. 
[N.S. Vou. XIII No. 318. 
disseminating a knowledge of the subject 
up to 1860. In 1850 he issued the first 
complete manual of fossil plants, giving a 
systematic account of 2,421 species. 
C. F. Schimper founded the theory of 
phyllotaxis. He first contributed to the 
study of fossil plants in 1840, and his 
‘Traité de paléontologie végétale’ consti- 
tutes the most important of all the works on 
fossil botany as presenting a complete man- 
ual of the subject in accordance with the 
then current ideas of botanical science. 
Williamson has contributed to the ad- 
vance of paleobotanical knowledge in so 
many important ways, especially during his 
later years in conjunction with Carruthers, 
that a preliminary statement of progress 
would be wholly incomplete without refer- 
ence to his work. His earliest experiences 
were gained in making the illustrations for 
‘Lindley and Hutton’s Fossil Flora of Great 
Britain in 1837.’ Since then his time was 
largely devoted to independent research in 
the same field, with a success which is well 
known, and his studies of the carboniferous 
flora of Great Britain have resulted in most 
important contributions to our knowledge 
of those early types of vegetation. This is 
especially true with respect to the Calama- 
rieae, Lepidodendreae, Sphenophylleae, the 
ferns and Lyginodendron. In the case of 
the first two, more particularly, he laid 
the foundation for all our subsequent 
knowledge respecting them. He further- 
more showed that in Lyginodendron the 
fructification places this group of plants 
beyond question among the archegoniates, 
but that like recent Gymnosperms, they 
possess a secondary wood growth from a 
cambium layer. In establishing this fact 
he came into direct contact with the views 
of Brongniart, who held the formation of 
the wood from a cambium layer to be an 
absolute criterion of the phanerogams. 
From Heterangium and Lyginodendron he 
reconstructed a type of plant which he de- 
