G. M. Thomson. — On the Fertilization of Flowerinrj Plants. 269 



but they are white aud secrete a minute trace of honey, and are therefore 

 probably visited by insects. The latter plant, which is one of the smallest 

 flowering plants we have, is remarkable for exhibiting distinct dimorphism. 

 In one form the stigma is almost sessile on the ovary, in the other there is 

 a well-developed style. I have not observed a corresponding difference in 

 the stamens, which made me think at first that the difference was due solely 

 to the varying age of the flowers examined. This, however, is not the case, 

 as in young and old flowers alike the two forms are to be found, 



Nat. Ord. Compositje. 

 This very large and important order is represented in this part of New 

 Zealand by about sixteen genera, out of the twenty-four occurring in the 

 colony. The advantages possessed by flowers of this order by having their 

 florets crowded together, have often been insisted on, the chief of these 

 being the prominent appearance of the flowers when massed together, the 

 facility with which honey is obtained rendering them attractive to insects, 

 and the greater chance of cross-fertilization enjoyed by them, seeing that 

 an insect lighting on a flower-head is likely to come into contact with 

 several flowers at each visit. A further chance in favour of cross-fertiliza- 

 tion arises from the polygamous nature of the florets in each head, those on 

 the outside being usually pistillate only, while those within are hermaphro- 

 dite. In most of the sub-order Liguliflor*, the ray-florets are pistillate, 

 and it is worthy of notice that this is the reverse of what usually occurs in 

 dioecious or polygamous plants, for it is usually the staminate or male 

 flowers which are the most conspicuous. This will be found to be the case 

 in almost all the genera mentioned in the earlier part of this paper in which 

 separation of the sexes occurs. In those Composites which are frequented 

 by insects — and possibly in others — autogamy^-' or fertilization of a flower 

 by the pollen from the stamens of the same flower, is usually avoided by a 

 simple form of proterandry. The anthers, which cohere to form a tube 

 round the style, dehisce a little before the flower expands ; the pollen, how- 

 ever, is retained in the tube, where it has no access to the stigmatic surfaces 

 of the style, as these are in close contact. The style gradually lengthens 

 up, however, through the staminal tube, which it bursts open at the top, 

 and scatters the pollen out. After a time the stigmatic arms at its summit 

 separate, aud gradually recurve, in which position they protrude to some 

 distance from the mouth of the floret. This peculiarity of Composites and 



* " Flowers and their Unbidden Guests," by Dr. Kerner, (C. Eegan Paul & Co.) 

 This author also proposes to use the terms geitonogamy, for the fertilization of a flower 

 by pollen from other flowers on the same plant, and xenogamy, for the fertilization of a 

 flower by pollen from other plants. Both terms to be classed under the name allogamy. 

 He objects to the indeflniteness of the term " self-fertiHzation." 



