12 



average number of plants per population observed 

 to date is approximately 760; the total number of 

 plants observed in Montana to date is 

 approximately 13,000-15,000. 



Details regarding population size and condition 

 are summarized in Table 2 . 



3. REPRODUCTIVE BIOLOGY 



a. TYPE OF REPRODUCTION: Two methods of 

 reproduction are known to occur commonly in 

 the Orchidaceae: vegetative spread, and 

 sexual production of seeds (Williams and 

 Williams 1983) . It appears that reproduction 

 by seeds is the predominant mode of 

 population maintenance for Orchis 

 rotundifolia . Luer (1975) states that 

 "(a)fter watching a colony of this orchid wax 

 and wane and shift position for well over ten 

 years, (it was) concluded that the plants are 

 short-lived and depend upon reseeding to 

 maintain their numbers." 



b. POLLINATION BIOLOGY: Most orchid species 

 rely on insects, especially members of the 

 Hymenoptera and Lepidoptera, for pollination 

 and subsequent fertilization. In the 

 Orchidaceae, the anthers, containing the 

 pollen grains, are grouped in masses called 

 pollinia. When insects visit the flowers, 

 they come into contact with the viscidium, a 

 sticky disk connected by a stalk to the 

 pollinia. The viscidium adheres to the 

 insect, taking with it the pollinia, which 

 can then be carried on to another flower. 

 However, in cases where a flower is not 

 visited by an insect, the viscidium shrinks 

 as the flower whithers, pulling the pollen 

 masses away from the anthers to hang forward 

 above the stigma. Wind movement is then 

 sufficient to bring the pollen into contact 

 with the stigma, and self-pollination is thus 

 achieved (Williams and Williams 1983) . It is 

 possible that self-pollination is prevalent 

 in O. rotundifolia p as no insect visitors 

 were observed during field surveys in 1988. 



c. SEED DISPERSAL AND BIOLOGY: Upon maturation 

 of the capsules, the walls split upon drying 

 to release the numerous seeds they contain. 

 The seeds of orchids are very small, and are 

 typically dispersed by wind. 



It is well known that most orchids rely on a 



