PHANEROGAMIA. 



413 



insect escapes, dusted over with pollen which, in spite of ex- 

 perience, it proceeds to convey in like manner to another flower. 

 Those flowers which are ready for pollination have an erect posi- 

 tion, and the tube of the perianth is open above so that the insect 

 can readily enter; after pollination the peduncle bends downwards 

 and the tube is closed by the broad lobe of the perianth, so that 

 it is impossible for insects to enter flowers which have been fer- 

 tilised. 



In the flower of Epipactis (one of the Orchidacese), the anther is 

 situated above the stigma and does not shed its pollen in isolated 

 grains ; but when a certain 

 portion of the stigma (the abor- 

 tive anterior lobe), known as 

 the rostellum (Fig. 244 ft), is 

 touched, the two pollinia (p. 396), 

 together with a mass of sticky 

 substance (retinaculum) derived 

 from the rostellum, are removed 

 from the pollen-sacs, adhering 

 to the foreign body (Fig. 244 

 F, Ji). The insect creeps into 

 the flower to obtain the honey 

 which is secreted in the cavity 

 of one of the leaves of the peri- 

 anth, the labellum (Fig. 244 Z) ; 

 as it withdraws from the flower, 

 it carries away the pollinia on 

 its head, and on entering the 

 next flower, deposits them upon 

 the stigma. 



Fertilisation. As in other 

 plants, so here, the process of 

 fertilisation consists in the fu- 

 sion of the male and female 

 reproductive cells. The male 

 cell (see p. 407), whether it be 

 a sperrnatozoid or not, escapes 

 from the pollen-tube and enters 

 the oosphere ; the nucleus of 

 the male cell (male pronu- 

 cleus) and " that of the female 



FIG. 241. Epipaclis l+tifolia : A longi. 

 tudinal section through a flower-bud; B 

 open flower after removal of the perianth. 

 with the exception of the labellum, I ; C 

 the reproductive organs, after the removal 

 of the perianth, seen from below and in 

 front ; D as B, the point of a lead-pencil ' 

 tb) is inserted after the manner of the pro- 

 boscis of an insect ; E and F the lead- 

 pencil with the pollinia at ached ; fK ovary ; 

 t labellum, its sac-like depression serving 

 as a nectary ; n the broad stigma ; en the 

 connective of the single fertile anther ; p 

 pollinia ; Ji the rostellum ; x the two lat- 

 eral staminodes ; i place where the labellum 

 has been cut off ; * the gynostemium. (After 

 Sachs.) 



