43S 



RELA TION TO ENVIRONMENT, 



llif same, but the parts of the flower are in fives, instead (jf in fours as ii. 

 the Lluet. While the pollen of the short-styled priinuhis sometimes must 

 fall on the stigma of the same tlowcr, Darwin has found that such polleii is 



Fig. 457. 

 Dichogamous llowers of primula. 



not so potent on the stigma of its own flower as on that of another, an ad- 

 ditional provLsiou whieh tends to necessitate cross pollination, 



Tn the case of some varieties of pear trees, as the bartlett, it has been 

 found that the llowers remain largely sterile not only to their own pollen, or 

 pollen Kji the fluwers on the same tree, but to all flowers of that variety. 

 However, they become fertile if cross pollinated from a diflerent variety of 

 pear. 



851. Pollination of the skunk's cabbage. — In many other flowers cross 

 pollination is brought about tlnough the agency of insects, where there is a 

 difference in time of the maturing ot the stamens and pistils of the same 

 flower. The skunk's cabbage (Spathyema ftetida), though repulsive on 

 account of its fetid odor, is nevertheless a ver\' interesting plant to >tudv lor 

 several reasons. Earl}- in the spring, before the leaves appear, and in many 

 cases as soon as the frost is out (.)f tlie hard groun<l. the hooke<! beak of the 

 large fleshy spathe <if this phint pushes its wav through thr soil. 



If we cut away one side (if the spallie as shown in fig. 45Q we shall have 

 the flowering spadix brouglit closely lo \\v\\ . In tlus sjiadix tlie pistil of 

 each crowded flower has pushed its style througli between the plates of 

 armor formed by tlie converging ends of (he sepals, and stands out alone 

 with the brush dike stigma ready for pollination, while the stam<.ais of all the 

 flowers of this spadix ai'c )H't hidd(.'n boneath. The insei. t-- whicli pass fnnn 

 thr --padix of OTIC jilant to ;ui<4lirr wiH. in crawling over tlu- ]">r< ijccting 

 stigmas, rub olf some ol the polh-ii which lias In.-(.-n caui^ht \\hil(.- \i--itin"- a 

 ])lant win -re tin.' stamens are scattering their pollen. In this w .\\ ci'oss pollin- 

 ati<jn is brought about. Such flowers, in wluch the stigma is prep.ired 



