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Nicolas Malebranche and the Dutch microscopist Jan Swammerdam. Malebranche had
written in 1674 that:We may say that all plants are in a smaller form in their germs. ... It does not seem
unreasonable to say that there are infinite trees inside one single germ, since the germ
contains not only the tree but also its seed, that is to say another germ, and Nature
only makes the little trees develop.^43Preformationists applied the ideas of the French philosopher Descartes, who posited a
universe initially created by God but governed thereafter mainly by mechanical laws, to
the question of embryo formation and growth in the womb. Preformationists fell into two
camps: the ovists and the spermists. The ovists believed that the unfertilized egg already
contained a miniaturized version of the mature organism within itself, needing only to be
activated by the male semen. The first preformationists were all ovists who believed that
the embryos of all the people who have ever lived on earth, and who will be be born in the
future, were originally nested inside the ovaries of Eve, like an infinite series of Russian
dolls.^44 The spermists, on the other hand, believed that all the preformed embryos originally
resided in Adam’s sperm. Spermism achieved a degree of notoriety in 1694 after the Dutch
microscopist, Nicolas Hartsoeker, published a sketch of a homunculus (tiny human) curled
up in the head of a sperm. Although the sketch was only meant to illustrate the theory of a
homunculus, word spread that Hartsoeker had actually seen one in the microscope. Not to
be outdone, several other microscopists soon claimed to have seen homunculi inside either
a sperm or an egg— another example of the believing- is- seeing principle!
Ironically, it was Camerarius himself who provided the first unequivocal evidence
refuting Sturm’s preformationist theory of plant reproduction. As described in the
Epistola, Camerarius, following the example of Malpighi, conducted microscope studies
on the development of the embryo in the ovules of Papilionaceae (legume) flowers—most
likely pea or bean—and obtained results that not only supported the importance of pol-
lination in embryo formation, but also directly contradicted Malebranche’s and Sturm’s
theories. Camerarius first removed the petals and stamens from the unopened floral bud
at the earliest stages of its development to observe the initial “rudiment” of the immature
pod prior to the release of pollen from the anthers. By holding the tiny pod up to the sun
and then placing it under the microscope, Camerarius was able to see a row of tiny, green-
ish transparent vesicles (the unfertilized ovules) lining the young pod, each vesicle filled
with a clear liquid. These ovules were the future seeds of the pod.^45 He then dissected
flowers with intact petals and stamens that had been allowed to undergo pollination.
Soon after the pollen had been released from the anthers, Camerarius could detect a new
structure inside the ovule, which he described as an undifferentiated “green dot.” Over
time, the green dot increased in size and developed cotyledons (embryonic leaves) and a
radicle (embryonic root).
The embryo, according to Camerarius, did not simply unfold into a young plantlet by
enlargement, as the Preformationists claimed. As it increased in size, it underwent shape
changes that transformed it from a round dot into an embryo. Camerarius was thus an
early proponent of epigenesis, the idea that the embryo acquires its anatomical features