[Transcriber's Note: Two footnote marks [3] and [4] above in original
text, but no footnote text was found in the book]
This process of growth can take place only when living _protoplasm_ is
present in the cells of the plant. The substance we call protoplasm is
an albuminoid, like the white of an egg, and it forms the flesh of both
plants and animals. A living plant can assimilate its own protoplasm, an
animal must take it ready-made from plants. But a plant can assimilate its
food and grow only under the mysterious influence we call life. Life
alone brings forth life, and we are as far as ever from understanding
its nature. Around our little island of knowledge, built up through the
centuries by the labor of countless workers, stretches the infinite ocean
of the unknown.
_Gray's First Lessons_. Sect. VII, XVI, §2, §4, §5, §6, 476-480.
_How Plants Grow_. Chap. I, 119-153, Chap. III, 261-280.