204 Macfarlane—Current Problems in Plant Cytology. 
debated, the necessity for some critical standard of reckoning 
has doubtless been painfully felt. The possible transmission 
of characters has been debated, but the vaguest views have 
been expressed as to what such characters are. Or again, 
species have been described as new which differed only from 
some older type in the size or folding of some part, in its 
relative hairiness, in its prostrate or upright habit, or in certain 
color effects. 
One great occupation in the coming century will undoubt- 
edly be, the elucidation of the precise morphological details 
of varieties and species, as being the only correct guide to the 
evolutionary affinities of our plant groups, and the segregation 
of species within these. All this must be accomplished from the 
standpoint of the cell as the ultimate factor. Whether in the 
upbuilding of unicellular or multicellular hairs of definite 
structure, in the presence of definite pigments over certain 
areas, in the development of thickening zones and other 
structural features, precise information is only obtained when 
such are recorded in terms of cell life. It will then be possi- 
ble to classify plants on a natural plan, instead of as now by 
selecting one or two points of resemblance—not necessarily 
of morphological contact—as a taxonomic basis. 
When such data shall have accumulated, the student of 
plant evolution will be in a position to compare varieties and 
species morphologically, to inquire intelligently how these are 
related to their environment, and to determine the limits 
within which variation may take place in a given time or under 
given conditions. The small beginnings have already been 
made, the coming century will doubtless witness the great 
continuations. Problems of surpassing interest invite our 
attention. My earnest hope is that our Society shall aid in 
the solution of some of them, and that annual contributions 
of ever-increasing value will be made to its Proceedings, 
