As a phylogenist, I have often experienced that a relatively small number of scientifically working botanists realize the importance — or even the existence — of the factor time. It is true that many of them never come across that factor; for a man who through his microscope analyses the structure of a tissue, or a man who with the most delicate methods investigates the composition of organic compounds in a vacuole, the factor time is quite insignificant, as long as they keep analysing and do not ask where things come from (which they usually don’t). However, the changes which time may entail in the material investigated, are practically always interpretable in terms of reversibility or periodicity. They seldom or never evoke thoughts of a farther past than a few hours, days, or years. I have sometimes felt astonished, moreover, that even morphologists who study the ontogeny of organs to the minutest details consciously or unconsciously stop at what they cannot observe with their senses, directly or by the mediation of their instruments; the step from ontogenist to phylogenist seems to be a very wide one.