partial notion of them, as unsatisfactory as our estimate of what people really are, from merely looking at the outside of the houses in which they live. The outer form we may know and admire, the inner substance must ever remain for most of us a secret treasure house the value of which is certain, but the key to which we do not possess. CHAPTER II PLANT BEHAVIOR 1. LIGHT AND ITS IMPORTANCE TO THE PLANT Practically all that has been said in the first chapter relates to what plants are, their organs, or what we may call the architecture or plan of their framework. But what they do with this elaborate structure is as important as what we do with a house that may contain every modern improvement but is never a home until these things have been put to use. One of the chief concerns of any architect is to see to it that the house has as much sunshine by day and as attractive illumination by night as possible. Nature, that greatest of all architects, also sees to it that plants get the utmost necessary sunlight, but for a much more important reason than the mere attractiveness of sunshine, be that ever so beautiful. For light, the life-giver of all green things, is so absolutely essential to plants that experiments to grow them in the dark have always failed, and many gardeners now use electric light in greenhouses in order to prolong the short daylight of winter. It is the lack of light that makes celery blanch. Plants grown in the house inevitably turn toward the windows, even plants growing against a wall turn their leaves away from it--nowhere can one find living green things that do not find the light as surely and persistently as men try to get their food or their mates. Many examples of this could be given and must have been noticed by everyone.