1238 A TEXTBOOK OF THEORETICAL BOTANY 



pressure forces out some of the slimy contents 

 which collect pollen, in the same manner as the 

 pollination-drop of a Gymnosperm. On release 

 of the pressure the style springs back into its 

 normal shape and the drop of mucus, with the 

 pollen, is withdrawn into the interior, where the 

 pollen germinates. Viola is not unique in this 

 mechanism, but it is rare and Burmannia is the 

 only other example which can be cited. 



The stigmas of Crocus, though tubular in 

 form, are quite different from the above (Fig. 

 1 194). The three styles are united below but 

 free above and the three branches are flattened, 

 with inrolled edges, forming three brightly 

 coloured funnels. The actual stigmas are only 

 at the upper rims of these, where receptive 

 papillae are developed. Pollen tubes grow rapidly 

 down the interior of the funnels, a matter of 

 some importance as the styles are exceptionally 

 long. 



Allied in nature to the above are the petaloid 



Fig. 1 104. — Tubular stigmas of , r t • /t-- \ --r'l ^1 



Crocus. (After Van Tieghem:) Styles of 7m (Fig. 1 1 95). 1 hese three organs. 



B 



D E 



Fig. 1 195. — Development of the stylar branch and stigma in Iris. A, Young 

 stage with dorsal stigmatic groove. B, Later stage with free margins grow- 

 ing out. C, Mature branch-style, abaxial view with stamen in front; 

 stigma dotted. D, Section near base of styles showing downward con- 

 tinuation of stigmatic grooves. E, Section at top of ovary; styles united. 

 {After Engler-Prautl and Goebel.) 



