I do not, I think, overestimate the value of the results obtained, If I did, I would have published sooner. But I haven often thought that there might be in them matter for stimulating others to undertake this work in a more thorough way. Several botanists have confirmed me in this view. Still I could not well overcome my reluctance till, in June 1909, Prof. H. E. Douglas published a similar investigation in the Monthly Weather review. I then resolved to publish what I had, in some form or other, in the hope that my contribution might help that of Prof. Douglas in calling forth more fundamental work from others. I hoped to do this in a more extensive and thorough way than it was done in my lectures and to add some materials about the period 1879 up to the present time. — Other work, however, has always made me delay this plan, so that finally I felt that nothing would ever come of the matter unless I resolved to publish just my lecture in Pasadena. About the lecture itself I wish to make a few remarks.