1904 



A TEXTBOOK OF THEORETICAL BOTANY 





Fig. 1823. — Solarium tuberosum. Flowers illustrating pollination. 



See in text. 



tacle itself they are shining and look damp, giving the suggestion of nectaries, 

 though they are not secretory, and insects visit the flowers in their search 

 for nectar. The insect trying to find the nectar shakes pollen out of the 

 sacs on itself and cross-pollination may thereby be effected. 



In the genus Datura nectar is secreted at the base of the ovary and is 



concealed in the lowest, contrac- 

 ted part of the bell-shaped 

 corolla. The flowers (Fig. 1824) 

 are protogynous and are visited 

 by humble bees. The genus 

 contains fifteen species most of 

 which are shrubs, herbs or occas- 

 ionally trees in subtropical count- 

 ries. Stramonum is obtained from 

 D. stramonium, but the species is 

 also interesting because of the 

 mutant races which have been 

 discovered. Datura is one of the 

 few genera in which a mutant 

 with less than the basic number 

 of chromosomes has been dis- 

 covered. D. stramonium has four- 

 teen chromosomes but a number 

 of mutants have been found by 

 Blakeslee each corresponding to 



or,, • r^, the loss of a different single 



1024. — Datura stramonium. Howenng ° 



shoot chromosome. 



Fig. 



