PROCEEDINGS OF THE SUMMER MEETING. 81 



and the olBPspring of their union were more variable than those which 

 might spring from one parent, or which had no father and mother. The 

 more variable the offspring of any species, the greater are the chances that 

 many of them will find congenial or at least tolerable places in nature, and 

 the safer is the species in the contest for life. It is the opinion of some 

 modern philosophers — Weismann and his followers — that the entire use of 

 sex is to originate variation in the offspring. 



nature's tendency as to sex. 



There must be a general tendency in species toward unisexuality. All 

 the higher animals are male or female, and some of the plants are so, also. 

 The great majority of plants, however, are still hermaphrodite. All our 

 common fruits have what the botanists call perfect flowers, that is, those 

 which contain both male and female organs. Yet nearly all hermaphrodite 

 plants develop their male and female parts at different times, so that the 

 flower can not fertilize itself. This, we suppose, is in consequence of the 

 fundamental law that the constructive and destructive changes upon which 

 the female and male elements respectively rest — or anabolism and kalabol- 

 ism — can not proceed simultaneously. In most plants, self-fertilization is 

 prohibited or hindered by this simplest of all methods, the different or 

 alternate maturing of the sexual organs. But the plant often goes further 

 than this, and the pistil or female organ refuses to accept the pollen from 

 the same flower, or even from any flower on the same plant; or, to trans- 

 pose the statement, the pollen is impotent upon its own sisterhood of pistils. 

 It is difficult to account for the physiological origin of this impotency, 

 although we should expect that male organs which are prevented from fer- 

 tilizing associated pistils might in time develop pollen which would be inca- 

 pable of fertilizing them; but its use to the species is obvious, inasmuch as 

 it insures cross-fertilization and thereby tends to strengthen or revitalize 

 the species. Darwin was among the first to study this subject, and he pub- 

 lished a list of plants which are sterile with their own pollen; but none of 

 the fruits are in his list. 



development of sex in plants has been slow. 



This fact — the impotency of certain plants with themselves — is itself of 

 immense practical importance, but we are anxious to know if such charac- 

 ters are likely to increase among cultivated plants, and if the future holds 

 more perplexity than the present. We have found that as struggle for 

 existence increased and organisms became more complex, animals could not 

 afford to be hermaphrodite or bisexual, for all the surplus energy was 

 needed for the development of a single sex. Among plants, this separation 

 of the sexes has proceeded more slowly because of their exceedingly con- 

 structive or vegetative character, which supplies sufficient nutriment to 

 maintain both sexes in greater or less perfection. But the further we 

 develop fruits the greater is the energy required in the production of that 

 fruit, and the greater, it would seem, must be the tendency toward the sup- 

 pression of one sex in given individuals, or toward the evolution of unisex- 

 ual individuals. Now, it is highly probable that one of the first steps in 

 the separation of the sexes is a differentiation in their mutual relationships, 

 whether a difference in time of maturing of the sex-elements or in the com- 

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