26 MASSACHUSETTS HORTICXJLTURAL SOCIETY. 



flowers bloom earlier than the upper, the latter having the stigmas 

 protruding and having at the same time the stamens tucked away in 

 the corolla where they cannot fertihze the stigmas. The anthers 

 mature later than the stigmas. Unless fertilized, the stigma droops, 

 and the stamens then protrude, so as to be ready to fertilize the 

 stigma of another blossom or another plant. The qiiestion arises 

 how pollen can be carried from one flower to another. In the plan- 

 tain it must be by the wind, for the flowers are not attractive to in- 

 sects, and for the same reason all grasses and sedges are cross-fer- 

 tilized in this way. The Houstonia grows in little patches, and it is 

 found that in some of these patches all the flowers have protruding 

 st3'les and anthers low down ; while in others all the flowers have 

 short styles, and anthers high up in the throat of the corolla. 

 The flowers of the former cannot fertilize themselves, but must be 

 fertilized by the other kind. The pollen of many flowers is not so 

 potent to fertilize the ovules of that flower as the pollen from other 

 flowers of the same species. This has been well stated by Professor 

 Gray, as follows : — "In the blossoms of peas, beans, etc., gener- 

 ally little or no seed is set when insects are excluded, although the 

 parts are so disposed that the stigma must be dusted by the pollen 

 of the stamens enclosed with it ; when, however, such stigmas are 

 touched by the pollen of another flower it seeds perfectly." In 

 the madder, cinchona, and ipecac, the structure of the flowers 

 is similar to that of Houstonia. 



In the case of ipecac plants raised in greenhouses, seed very 

 rarely if ever sets. Professor Balfour was led to suspect the cause, 

 and he found plants of ipecac in the other dimorphous state — that 

 is with reciprocal styles — and by fertilizing one form with the other, 

 fruitful seed was produced. Lythrum Salicaria presents an ex- 

 ample of trimorphism, the stamens and pistils having three different 

 lengths with regard to each other and to the st3'les, and necessita- 

 ting the action of insect agency. The arrangement in the Scrophu- 

 lariacece, including the Gerardia, and also in the Gloxinia and other 

 gesneraceous plants, is the same as in the plantain, but these have 

 the addition of color to attract insects. One of the most remark- 

 able provisions to ensure cross-fertilization is seen in the Cleroden- 

 dron, so well known in our greenhouses. When the flowers first 

 open, the long styles are curved back and the stamens are straight, 

 l)ut afterwards the stamens curve back, and the style straightens, 

 and the ovules cannot be fertilized by tlie pollen of the same flower. 



