in Plant Cytology. 185 
detracting from Botany, should be accepted as evidence that 
the laws governing the life of every plant unit are the more 
complex and profound, and, therefore, the more worthy of 
closest study. Coincident with this advance were the studies 
of Naegeli and Briicke on cell structure and irritability, of 
Hofmeister on the evolutionary relation of cells and tissues in 
vascular plants, and of Herbert on hybridization. 
The third quarter of the century ushers in a galaxy of giant 
workers, who produced epoch-making works, all founded on 
cellular morphology and physiology. That this period is 
marked by the appearance of Darwin’s numerous contributions 
is ample testimony to its fruitfulness. The works of Berkeley, 
de Bary, Tulasne and Brefeld on the Fungi, of Schwendener 
on the Lichens, of Hofmeister on the vascular plants, and of 
Sachs on general physiology were rendered possible only by 
recognition of the cell as the fundamental unit of plant life. 
The advances of the quarter century that has now nearly run 
its course are known to all, but the outstanding feature of the 
period has been the remarkable increase in the number of 
workers who are contributing their share to the common 
stock of morphological and physiological knowledge. No 
previous quarter of a century in human history has equaled 
the present in the variety, wealth and novelty of results. 
Let us attempt now to survey our present day knowledge, 
and inquire regarding lines of progress for the future. A 
proper conception of plant cytology at once brings before the 
mind groups of problems, any one of which already claims 
the attention of specialists from the multiplicity of details that 
bear on it. It may seem presumptuous, therefore, on my part 
to attempt to review and compare the studies which have 
already appeared, but every teacher of his science must 
accomplish this more or less perfectly. Though a somewhat 
arbitrary method, I may be permitted, as a matter of con- 
venience, to glance at cell life from the standpoints of (a) 
