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excluded and I further pointed out, that from these results there can 
be no question of a natural law in the sense imagined by Darwin. 
Furthermore, the view that cross-fertilisation might be advantageous 
to the species, has been rendered untenable by our present knowledge 
of the structure of the nucleus, and its function in the life of the plant, 
and also by our modern ideas concerning the nature of fertilisation. 
Suppose we now give up this view, and fall back on the funda- 
mental hypothesis, which was put forward by GArrner in 1849, that 
only by self-fertilisation, vigour and fertility of the species are pre- 
served, since a cross may lead to hybrid-formation, which diminishes 
the fertility of the plant. It then follows, that floral biology, which 
has started in its considerations from the opposite view, has lost its 
basis and must be built up anew. We have been led astray by 
our ideas regarding the significance of the properties of the perianth 
— its shape and dimensions, its colour and odour — and regarding 
the various mechanisms of the flower — dioecism, monoecism, hete- 
rogamy, dichogamy, hercogamy and self-sterility — all of which we 
thought we could explain as useful adaptations for visiting insects 
in order to ensure cross-fertilisation; it must be possible to explain 
them in another way. I have already sbown in my previous paper 
that diclinism and hereogamy can be explained by mutation and 
that protandry and protogyny must be considered as characters of 
organisation, and not of adaptation. 
With regard to the phenomenon of self-sterility I limited myself 
to pointing out, that this should be considered primarily as the result 
of hybridisation, rather than as a special adaptation. 
In order that we may now obtain a better conception of the 
qualities of the floral envelopes, we must again adopt the view of 
the older biologists, who regarded these envelopes as organs for the 
protection of the sexual apparatus. 
We must therefore consider to what extent the sexual organs 
require the protection of the perianth, not only when they originate 
and develop, but also during the flowering period. Hitherto we have 
been accustomed to look for a connexion between the various pro- 
perties of the perianth and its significance in the attraction of insects. 
Now we shall have to test these same properties, especially of shape, 
dimension, position and the distribution of fragrant vapours, by the 
question, how they may be considered to be of importance to an 
organ, which is intended to protect the sexual organs from unfavour- 
able external influences. More than has hitherto been the custom in 
floral biology, we shall have to pay attention to the anatomical 
structure and the physical and chemical properties of the floral 
