84 CHAPTERS ON EVOLUTION. 



occasionally fully developed ; whilst another plant of the order 

 ( Verbascum} possesses five stamens as its constant provision. Unless, 

 therefore, we are to maintain that nature is capricious beyond our 

 utmost belief, we are rationally bound to believe that the rudimentary 

 fifth stamen of Scrap hularia, and the absent fifth stamen of other 

 plants of its order, present us with an example of modification and 

 suppression respectively. The now rudimentary stamen is the repre- 

 sentative of an organ once perfect and fully developed in these 

 flowers, and which is perpetuated by the natural law of inheritance 

 until conditions, to be hereafter noticed, shall have caused it to entirely 

 disappear. The case for the natural modification, and that against 

 the imperfect creation of such flowers, is proved by an ingenious ex- 

 periment of Kolreuter's, upon plants which have the stamens and 

 pistils' situated in different plants, instead of being contained in the 

 same flower, as is ordinarily the case. Some "staminate" or stamen- 

 possessing flowers had the merest rudiment of the pistil developed, 

 whilst another set had a well-developed pistil. When these two 

 species were "crossed "in their cultivation, the "hybrids" or mule 

 progeny thus produced, evinced a marked increase in the development 

 of the abortive organ. This experiment not only proved that, under 

 certain conditions, the rudimentary pistil could be improved and 

 bettered, but also confirmed the identity of the two pistils, and the 

 high probability that the abortive organ in the one flower was simply 

 the degraded representative of the well-developed part of the other. 



As a final example of the manner in which we receive clues 

 towards the explanation of the modifications of flowers, the case of 

 the wallflower is somewhat interesting. This plant and its neigh- 

 bours possess the parts of the flower in fours (Fig. 23, A). There are 

 four sepals and four petals, whilst six stamens (Fig. 23, B) are de- 

 veloped ; the pistil possessing only two parts. Here the law of 

 symmetry would lead us to expect either four stamens or eight 

 the latter number being a multiple of four. The clue to this modifi- 

 cation is found . in the arrangement of the stamens. We find that 

 four of the wallflower's stamens are long (Fig. 23. B, j/'), whilst two 

 (si 2 ) are short. The four stamens form a regular inner series or 

 circle, the two short stamens being placed, in a somewhat solitary 

 fashion, outside the others. This condition of matters points probably 

 to the suppression of two of an originally complete outer row of four 

 stamens, and we receive a clue concerning the probability of this 

 view by finding that in some other flowers of the wallflower group the 

 stamens may be numerous. 1 It is hardly within the scope of the 

 present chapter to say anything regarding the causes of the conditions 



1 It is proper to mention that other explanations of the existence of two short 

 outer stamens in Cruciferez are known to botanists. That here given appears, 

 however, to be equally acceptable with more elaborate theories of this condition. 



