360 



PLANT LIFE. 



provision for welcome guests must be enumerated the meth- 

 ods of excluding unwelcome guests, which on account of their 

 size and habits are unable to bring about the desired transfer 

 of the pollen, while at the same time they rob the plant of 

 nectar or pollen provided for more acceptable visitors. 



Fig. 403.— Flower of Cobaa scandens, halved; showing tufts of hairs on the base of 

 the filaments, of which there are five ; these close the bottom of the corolla cup where 

 nectar is secreted against intruders. Three-fifths natural size. — After Kerner. 



(i) Various obstructions with- 

 in the flower may render ac- 

 cess to the nectar impossible 

 to the smaller and weaker in- 

 sects, while allowing others 

 to reach it. Such obstruc- 

 tions are formed by folds, 

 hairs, and other outgrowths 

 upon the flower leaves or the 

 essential organs (fig. 403). 

 (ii) Obstructions outside the 

 flower may exclude crawling 

 Such are sticky sur- 



by the numerous sticky glandular hairs on f aceg an( J ^US (fig. 404), 

 the flower stalk, ovulary, and calyx. Mag- v ° t ~rn 



nified several diam.— After Kerner. moats about the Stem formed 



by cup-shaped leaves holding water, or those formed by 

 water in which swamp plan Is grow, (iii) The time of bloom- 



Fig. 404. — Flower of a saxifrage {Saxifraga jnsectS. 

 controversci), protected against invasion 



