30 IOWA ACADEMY OF SCIENCES. 



biologists, even, down to nearly the middle of our century, he 

 could not conceive of a natural system as we understand it in 

 the light of evolution. To him a natural system was a thing 

 of the future, and it would represent the plan of the Creator. 

 His systems were predominent to about the end of the century, 

 when they were succeeded by others, framed in the attempt to 

 form a natural system, and to provide place for the enor- 

 mously increasing numbers of known plants and animals of 

 the lower orders. Most of the elements of our present biology 

 had a vigorous beginning in the seventeenth century, but 

 little advance was made during the eighteenth century, and 

 this was mainly due to two causes: the influence of Linnaeus 

 that turned the attention of men to classification, and the tend- 

 ency toward excessive speculation in the eighteenth century, 

 observable in the history of all sciences, and having its founda- 

 tion in the general belief that a System of Nature was some- 

 thing to be thought out by a priori reasoning. 



The first man to observe vegetable cells was probably 

 Robert Hooke, in 1667, not as a botanist, but as one interested 

 in showing the power of the microscope. The first to study in 

 a broad way the minute anatomy of plants, and to describe the 

 structure of plant and animal tissues, were Malphigi and Grew, 

 1670-82. They did not, however, regard the cell as the unit of 

 plant and animal structure, or from a cell theory. Beyond 

 some work by Wolff, in 1759, who attempted to found a cell 

 theory, little was added to the work of Malphigi and Grew 

 ,until 1801, when the subject was taken up by Mirbel. The 

 first cell theory wo thy of the name was proposed by Schlei- 

 den, according to which the cell is the unit of all plant tissue; 

 and in 1838 the theory was applied to animals, by Schwann. 

 The physiology of the cell, in essentially its present form, 

 was given by Nageli, only after protoplasm was investigatp.d 

 by Von Mohl, in 1846, and Schultze and De Barry recognized 

 it as the essential part of the cell. The essentials of our 

 theory of the origin of tissues and their classification were 

 worked out between 1820 and 1860. 



The history in time of the theory of reproduction is long 

 and interesting, both from the scientific and the psychological 

 point of view. Strange as it may seem the fact of sexuality 

 in plants was first definitely asserted and scientifically main- 

 tained by Comerarius about 1694, but his work was lost sight 

 of until republished 100 years later. Despite the seemingly 



