While the cause of mutants has not yet been revealed, we have already seen that the two remaining kinds of variability are due to changes in the environment, or to crossing. Charles Darwin when he published his “Origin of Species,” than which no other book has so completely revolutionized modern thought, did not state the cause of those variations of which he was our greatest observer. He did state the now universally accepted law of the “Survival of the Fittest” which explains how, once these variations make their appearance, the inexorable conflict of nature would automatically weed out the unfit. We have seen all through the course of this history of the plant kingdom how whole types of vegetation have been overthrown to give way to other types better fitted to survive. That process is going on with just as inexorable results to-day as it has down through the ages. While Darwin never claimed that such a purely selective process could initiate new species, many of his partisans who waged battle for him during the first years of the tremendous opposition his views encountered, did so claim, and probably wrongly. The actual cause of the origin of new species, except those demonstrated to result from new combinations of already known characters, through crossing, cannot be explained through the natural selection of plants or animals which exhibit favorable variations. We see their effects; it is obvious enough, that those of value tend for the survival of plants having such variations, and it was natural enough that older students of the problem should mistake these effects for the cause of them. The process of selective elimination constantly going on does tend to fix certain favorable variations and untold millions of plants have had their day in the past due to their possession of such, and the killing off of their less fortunately provided associates. We speak of this great march from the simplest organism up to our most complex plants and animals as their evolution, but we must never forget that it has gone step by step, by one or the other methods by which we have seen that plants vary, or perchance by some undetected method, and that while the results of it are for all to see, the causes of that infinitely slow and quite often wayward variation are not understood. Upon such a conception our modern plant life is seen to be a development of plants that have gone before, that all existing life is derived from preexisting, and not from providential interposition or special creations. All through the long marches of plant evolution there appears to be a definite and final goal toward which it tends, but we do not know the direction, least of all the object, of that goal. In fact, there may be many goals, just as there are the diversity of ambitions among human beings. In tracing the present ascendancy of our flowering plants from their links with the past perhaps we shall find no better statement of their present