88 



Elementary Work in Botany. 



Fig. 66. Silver bells 

 (Calochortus albus). 



flower often depends greatly upon light, heat, and moisture; 

 or, in other words, upon the time of the day 

 and the kind of weather.* In describing 

 flowers we should give the positions and 

 forms when most actively at work, with ban- 

 ners widely spread, nectaries open, and 

 stamens ready to give pollen, or the pistils 

 waiting to receive it. 



The form of a flower depends upon the 

 inclination 



of its conspicuous parts 

 or the lobes of these when 

 united to the axis or ped- 

 uncle, as well as upon their 

 shape and adhesion or co- 

 hesion. For example, the 

 sepals of clematis and the 

 corolla lobes of trientalis, 

 spreading at right angles to 

 the floral axis, form wheel- 

 shaped or rotate flowers ; the 

 perianth of crown-imperial 

 or of our most common fritillaria and the corolla of cain- 



*Some flowers are open at night only. Most flowers droop and partly close 

 in the rain. Pupils should study the behavior of plants in their homes out of 

 doors. Often the appearance of a plant changes greatly after it is plucked and 

 brought into the house. 



Some of the resting positions or shapes of the floral organs are interesting. 

 The corolla of a morning-glory, for example, when it quits work covers the stig- 

 mas with a cap very unlike that which crowned the bud. And there is a reason 

 for this. 



Fig. 67. Regular corollas with united petals. 

 Tubular corolla of tree-tobacco (Nicotiana 



flauca). b. Salverform corolla of slender tobacco 

 Ntcotiana attenuata). c- Rotate corolla of sola- 

 uum. d. Campanulate corolla of blue-bells. 



