On the Structure and Pollination of the 



Flowers of Eupatorium ageratoides 



and Eupatorium coelestinum. 



By Laura B. Cross, Ph. D. 



(With Plate XVIII.) 



IN the contributions that are being made to plant polli- 

 nation, the relative frequency of self and cross polli- 

 nation has received a considerable share of attention. 

 The fact that various flowers, once regarded as being 

 probably cross-fertilized have, during recent years, been 

 found to be systematically self-pollinated ; and also the 

 increasing number of plants that have been shown to bear 

 cleistogamic flowers, both point to the necessity for accu- 

 rate statistics, not only for the orders, but for the species 

 composing them. No order, probably, has received more 

 attention than the Compositae ; but much remains to be 

 done in the extended study of the different genera and 

 species. The following is a contribution toward the study 

 of Eupatorium suggested by Dr. Rothrock in 1891. 



H. Miiller* has given some details, structural and physi- 

 ological, of his observations on Eupatorium cannabinum ; 

 and though the species I have examined differ in specific 

 details, the fundamental points established by him have 

 been confirmed by my observations. 



Twelve plants of Eupatorium ageratoides and twelve of 

 Eupatorium coelestinum were selected and subjected to the 

 same treatment throughout. Four plants of each were pro- 

 tected by thin cotton cloth, and four by coarse Swiss 

 muslin, at a time when the flower parts were immature 



*" Fertilization of Flowers," Eng. Ed. 1883, pp. 318-320 ; 363-364. 

 260 



