io6 NATIVE BRITISH ORCHIDACE^ 



Corallorhi^a, in which the fungus estabhshes itself from the beginning, entering the 

 seed by way of the suspensor, permeating the rhizome and malting its way into all 

 roots as they appear.' 



Fertilisation. The anther opens in bud, and deposits the poUinia on the upper 

 surface of the horizontal rostellum. In a newly opened flower no viscid gland can 

 be seen, but the pollinia lie quite free, their thin upper ends forward in the groove 

 of the rostellum, the tip of which turns down a little, leaving a slight space between 

 itself and the ends of the pollinia. It was found that if the underside of the rostellum 

 was gently stroked in an upward direction with a camel's hair brush, or touched with 

 a needle, a large drop of milky looking liquid was instantaneously ejected, big enough 

 to fill up the space between the end of the rostellum and the tips of the pollinia, which 

 were caught and held by it. This drop was sufficiently viscid to adhere to the touching 

 object and to bring with it the pollinia, rapidly setting brown and hard like cement. 

 The simplicity and" never-failing efficiency of this ingenious device are most striking. 

 The mechanism is identical with that of Listera. 



The adhesive liquid is contained within the cells of the rostellum. Darwin states 

 that there are about six rough points on the crest of the rosteUum which seem par- 

 ticularly sensitive to a touch, causing the expulsion of the viscid matter.^ After about 

 four days the rostellum loses its sensitiveness, and fails to eject the liquid. Its tip 

 turns black, and a hard ball of matter can be seen and felt— the viscid material has 

 set hard in situ. After the flower has been open for a few days the pollinia swell and 

 disintegrate, overhanging the sides of the rostellum, and sliding down on to the 

 stigma which lies immediately beneath. This gives rise to self-fertilisation, a result 

 also brought about by the presence of minute insects (thrips), which may be seen 

 crawling about the flowers dusted all over with pollen.^ 



Insects are attracted by the honey-like smell, and the tiny drops of nectar on the lip 

 eventually lead them to the cup at its base, where it is more plentiful. They thus touch 

 the sensitive rostellum, and the pollinia become cemented to the head or thorax. 

 Hermann Miiller saw the plant visited by flies in considerable numbers, and several 

 of the spikes were covered with spiders' webs. He saw Spilogaster cinerea and small 

 Muscids sucking the honey, but without removing the pollinia. Finally he saw a 

 larger yellow fly i^elotny^a affinis Mgn.) crawl up the lip to its base, licking the honey 

 on its way, till it came in contact with the rostellum, thereby cementing the pollinia 

 to the froiit of its thorax. It flew away, startled, but was caught in a spider's web.3 

 One cold wet season Darwin could not find a drop of honey, though he searched 



several times. 



We noticed that in a number of flowers (but not in all) after a time the rostellum 



I Weiss, Presidential Address, Manchester Micr. Soc. (1917)- 



» Vert. Orch. ed. 2, pp. 125-6. 3 H. Miiller, Vert. oJVlowers, p. 532. 



