May 10, 1912] 
also becoming unconsciously a draughtsman, 
and when required, as he should be, to produce 
with pencil what he sees, if he wants to do it, 
he will do it instinctively.” Lastly, Clark had 
in view graduate courses for advanced work 
and for special training. 
His work was now interrupted by a severe 
illness. Never robust, his assiduous and con- 
fining labors had seriously impaired his health. 
As early as 1857 are entries in his diary of 
symptoms indicating that the seeds of the dis- 
ease that was to cut him off in his prime were 
then sown. After much suffering, on the first 
of July, 1878, at the age of forty-seven, his 
useful life came to an end. He was a mem- 
ber of the leading scientific societies in this 
country, including the National Academy of 
Sciences, which up to that time was limited 
in membership to fifty of the foremost scien- 
tists of the country. 
His first love for science, writes one who 
knew him well, seems to have grown from 
his fondness for flowers. After he became a 
student of Professor Agassiz his love for bot- 
any remained undiminished. He studied it in 
after years from the side of vegetable histol- 
ogy and morphology in connection with and 
as illustrating the histology and morphology 
of animals. The influence of his knowledge 
of botany on his zoological studies was 
marked. It prepared him for his studies on 
spontaneous generation, on the theory of the 
cell, on the structure of the Protozoa and the 
nature of protoplasm. In studying the lasso- 
cells of the acalephs, he traced their analog- 
ical resemblance to the stinging hairs of the 
nettle. By his intimate knowledge of the 
spores of the smaller alge he was able to 
point out some of the characters separating 
the lowest Protozoa from the spores of plants, 
and aid in the work of Thuret and others in 
eliminating from the animal kingdom certain 
vegetable spores which had been originally 
deseribed as Infusoria, 
In his first scientific paper, communicated 
by Dr. Gray in 1856, he showed that in most 
of our North American gentians the ovules 
are spread over the whole parietes of the ovary, 
either irregularly or in vertical lines on the 
SCIENCE 
727 
veins. His next paper was on the peculiar 
growth of rings in the trunk of Rhus towi- 
codendron, and this was supplemented by 
further studies on the eccentricity of the 
pith of Ampelopsis quinquefolia and Celastrus 
scandens. He made experiments for a series 
of years on the value of the bark to the life of 
the tree. He observed the relation and de- 
velopment of the filaments which connect the 
anthers to the sepals of Comandra umbellata. 
In his paper on the identity of the vibrios and 
the muscular fibrillz, he showed how the latter 
during decomposition break up transversely, 
the fragments assuming the form and move- 
ments of the former. He also made observa- 
tions on the absorption of albumen in the cells 
of plants. His last purely botanical paper 
(1859) was on the nature of the glandular 
dots of the pine. His skill in the use of the 
fine lenses made by Spencer (under his direc- 
tion) enabled him to see more than his prede- 
cessors of the true relations of these dots. 
But his botanical studies did not end here, as 
may be seen by reference to his diaries and 
his frequent allusions to the lower alge and 
to vegetable histology in “ Mind in Nature.” 
In his walks he often botanized, and contrib- 
uted in this way to Gray’s botanical text- 
books. Thus with the training he received 
from Gray and Agassiz, he looked upon the 
world of organized beings from both the 
botanical and zoological side. He well de- 
serves the name, biologist. 
Between 1856 and 1863 he was associated 
with Agassiz in the preparation of the ana- 
tomical and embryological portions of the 
great work entitled “Contributions to the 
Natural History of the United States.” To 
these volumes he was a large contributor, most 
of the histological and embryological por- 
tions of the work being his, and more than 
half the plates illustrating the embryology 
and histology of the turtles and acalephs bear 
his name. “In the preparation of this part 
of my work,” says Professor Agassiz, “I have 
received much valuable assistance from my 
friend and colleague Professor H. J. Clark, 
who has traced with me, for more than nine 
years, the metamorphoses of our Acalephs, 
