138 BOTANY. [CHAP. iv. 



still free from each other. Well-known examples are, 

 violets (Violacece) ; peas, beans, and vetches (Legu- 

 minosce) ; and orchids (Orchidacece) . In the last-named 

 order there is a sequence from self-fertilized plants to 

 others that display the most perfect arrangements for 

 cross-fertilization met with in the Vegetable Kingdom. 

 Orchids belong to the same division of Angiosperms as the 

 lilies Monocotyledons and, like the latter, belong to the 

 type of regular flower with three free sepals, three free 

 petals, six stamens, and a pistil consisting of three carpels 

 grown together. The common tiger lily still shows this 

 structure, but the orchids, which may be said, as a group, to 

 have devoted their whole energy to the perfection of the 

 method of cross-fertilization with the greatest amount of 

 certainty combined with the minimum expenditure of 

 material, have developed an irregular flower. This 

 irregularity in the simplest type consists in the modifi- 

 cation of form of one of the three petals, the posterior or 

 uppermost; this modified petal is known as the lip or 

 labellum. In other species more of the sepals and 

 petals become changed, and there is a general tendency 

 on the part of the flower to become compressed laterally, 

 thus shadowing in the tubular type of flower, open at 

 the mouth and becoming narrower downwards towards 

 the point where the stamens and pistil are situated ; the 

 object of this arrangement being to compel the insect, 

 when sipping the nectar, to bring some portion of its 

 body in contact with the stamens or stigma as the case 

 may be. In such flowers the lowermost or anterior 

 petal is usually large, and stands out as a landing stage 

 on which the insect alights. A curious feature in the 

 evolution of the flower in orchids consists in the fact 



