44 PLANTS OF NEW ZEALAND 



and structure of the flower depend to a larye extent on the 

 nietliod of polhnation adopted In- it. 



These methods are very numerous, and often very different, 

 and a great deal of complexity of contrivance, and apparent 

 purposefulness of action, is manifested by flowers m their 

 endeavours to secure effective pollination. If the pistil is 

 pollinated from its own stamens, it is said to he self-pollinated. 

 Darwin and others have shown, that, as a rule, seed (.")btained 

 from cross-pollmated flowers is healthier and more productive 

 than that from self-pollinated flowers. The result of continued 

 mlireedmg is harmful to flowers as well as to animals ; but 

 there are probably more exceptions to this rule than was at 

 flrst supposed ; and m many plants there are special adapta- 

 tions for self-pollination. Cross-pollination ina>' be brought 

 about by the action of wind or insects, or, more rarely, by 

 l)irds or other animals. 



The exact methods adopted will be discussed in connection 

 Avith speciflc cases. 



If stamens and pistil are found in one flower, it is said to be 

 lirDiiaplirodite. If they are fV)und on dift'erent flowers but on 

 the same plant, the s[)ecies is then said to be iitvitwcious, but 

 if 1111 different plants, it is termed diwcioiis. 



The Flohal Envelopes. 



Surrounding the stamens are usually two floral envelopes. 

 4'lie outer one is the cali/x, and the inner is the corolla. The 

 corcjlla IS usually brightly coloured, and serves as an organ of 

 attraction for insects and other animals. The individual 

 leaves of which it is composed are termed petah. They may 

 be free or united, regular (.)r irregular in form, and, indeed, 

 manifest an mflnite variety of shape, colour, texture and 

 arrangement. These characteristics depend almost entireh- 

 upon the adjustment of the flower to the function of pollination. 



