246 BOTANY. 



517. These differences in the sexual organs are accom- 

 panied by similar ones in the surrounding parts. Thus 

 the stamens and pistils in grass-flowers are surrounded by 

 chaffy scales pale or green in color. Such flowers are 

 therefore not conspicuous, although generally clustered at 

 the summit of the stem. Moreover, they possess little or 

 no nectar, and, with few exceptions, are scentless. In the 

 Orchids there is a well-developed perianth which shows 

 high specialization of form and color. Most are provided 

 also with nectar-glands and an attractive odor. 



518. In Orchid-flowers the stamens and styles are fused 

 together into a "column" which occupies the centre of the 

 perianth. In the great majority of cases there is but one 

 anther (representing one stamen), and this is on or near the 

 end of the column, so placed as to be readily touched by 

 an insect entering the flower. The pollen-cells cohere in 

 little sticky masses, which easily adhere to the head, an- 

 tennae, or back of an insect. 



519. It is an interesting fact thai in the ordinary terres- 

 trial Orchids the flower develops in such a way that it must 

 twist upon its ovary in order to attain its proper position 

 when open (Fig. 138). Thus, without twisting, the lip {t) 

 with its spur would be uppermost, while the anther would 

 be below. 



520. When a long-tongued insect is attracted to an 

 Orchid-flower by the color and odor, it thrusts its tongue 

 down into the spur (sp) in search of nectar or sweet juices, 

 in the mean time perhaps resting its feet upon the lip {t). 

 Its head comes in contact with the sticky discs (at h), which 

 adhere tenaciously. "When the insect withdraws its tongue, 

 it at the same time carries away the pollen-masses adhering 

 to its head. When the insect visits another Orchid-flower 



