August 1, 1891.] 



KNOWLEDGE, 



151 



of fertilization of Hahemaia chlorantha, the Butterfly 

 Orchis. It is quite a common form, flowering during 

 June and July in meadows and on heaths. It is noted 

 for its fragrance and for its pure white, but generally 

 greenish-yellow flower {■x^-mpoi, green, and avSos, a flower). 

 The spur is very long, at least twice the length of the 

 ovary. The labellum is strap-shaped ; hence the name 

 Hnlicnariii (ltah<na, a thong) according to some authors, 

 although Hool?er says the etymology is doubtful. 



The connective is largely developed, so that the two 

 anther-lobes are very much separated, especially at the 

 base (Fig. II.). The discs of the poUinia are thus far 

 apart. The viscid matter is not enclosed in a pouch as in 

 Orvhu mascula, but is free on the under surface of the 

 discs which face one another (Fig. 11. </.). These occupy a 

 position anterior to the two united stigmas situated beneath 

 (Fig. II.). Another curious arrangement is seen here. 



fevf 

 petals 



•ubber" 



-Stc^ma. 

 '-..entrance lo 



FiQ. II. —Front - 



ri- of llahi.m.n 

 Orchis). 



of flow 

 (Butterflv 



Instead of the caudicle being attached at once to the disc, 

 it is hinged to a small process that arises perpendicularly 

 from the upper surface of that organ, and is called the 

 jx'dirct. The pollinia lie far back in their cells, so that 

 the caudicles are slightly bent. In their natural position 

 each caudicle is at right angles to the pedicel, and con- 

 sequently parallel to the viscid disc (Fig. III., 1, 2). The 

 nectary is generally two-thirds full of nectar, and so is 

 visited frequently by insects. The fragrance of the flowers. 



L-ctV-i'ficlt 



f OVA R Y 





Kiu. lll.^JIahciaria chturaiillia. The parts are as noteil in tlio figures 



and their light colouration, admirably fit them for the 

 \'isits of insects that fly by night. These are in this case 

 moths. It frequently happens that, on accovmt of the 

 distance between the discs, only one poUinium is removed 

 at a time. They are often found adhering to the eye of 

 the insect. The \-iscid matter does not set hard' im- 

 mediately, but is of such a nature as to fix the poUinia 

 firmly to the head of the intruder without setting. 



It is clear that unless some movement of the poUinia 

 takes place after their fixation to the insect's head, that 

 fertilization will not be eftected. The pecUcel performs 

 the needful act. It contracts along one side, and at the 

 same time moves through an angle of nearlj' 90^, dragging 

 the pollinia inwards and downwards, and in the exact 

 position to strike against the stigma when next an insect 

 visits a flower of the same sijecies. 



As the viscid material does not require to be set hard, 

 but performs its office immediately, there is no puncturing 

 of a nectary required to detain an insect ; instead, there 

 is a free supply of nectar. 



The structure of the Orchid flower is quite anomalous, 

 but it can be reduced to the normal type, though it requu-ed 

 the genius of Darwin to work it out. The parts of a 

 flower are generally developed in whorls, and the members 

 of one whorl alternate, as a rule, with those of the adjacent 

 whorls. Exceptions to this rule can generally be ac- 

 counted for by displacements that have occurred during 

 the development of the floral parts. The significance of 

 the organs of the Orchid are more difficult to determine. 

 Darwin accomplished the task by counting the groups of 

 bundles of spiral vessels that proceeded from the ovary. 

 These are in part the constituents of the veim of a leaf. 

 Their presence would denote the presence of a leaf or 

 modified leaf at an early stage in the development of the 

 flower, as they are generally the first diSerentiation exhi- 

 bited in the tissues of a growing mass of cells of a higher 

 plant. 



Fig. IV. is the result of his labours in this direction. 

 In Orchis ituiscula and Hahenaria ^ 



rlilomnthi, and in all Orchids, with 

 the exception of the Cupiijicdinnis, 

 there is only one fertile stamen — 

 the posterior one of the outer whorl. 

 The other two belonging to this 

 whorl have become united to the 

 anterior petal to form the labellum. 

 Of the three stamens of the inner 

 whorl none are represented in the 

 Orchids whose fertilization we have 

 described. In Cypripcdiinii the two 

 lateral stamens of the inner whorl 

 are the fertile ones, while the pos- 

 terior stamen of the outer 

 whorl forms a large head 

 which projects above them. 

 When the third stamen of 

 the inner whorl is present, it 

 unites with the anterior por- 

 tion of the colunm, and so 

 acts as a support. 



There are three stigmas cor- 

 responding to the three groups 

 of ovules in the ovary. But 

 only two of the stigmas act as 

 sucli ; the posterior one is 

 modified to form the rostellum, 

 whose viscid matter has been 



formed in the colls of which it was originally com- 

 posed, and which have afterwards broken down. 



Fig. IV. — Ground 

 plan of typical Orchid 

 flower. 1, 2. 3, sepals, 

 1 is the ]>ost(>rior sepi\l ; 

 1', 2', 3', petals. I' is the 

 anterior petal ; A, B, C, 

 out<'r whorl of stamens. 

 B and C are united to 

 the anterior petal and so 

 help to fonu the label- 

 hun ; -V is the fertile 

 stamen in all Orchids 

 with the exception of 

 Ciipripedium ; D, E, F, 

 stamens of inner whorl, 

 none of which arc pi-e- 

 sent in Orciis masriila 

 and Hohpuaria chlor- 

 antha — in Ctfpripedium 

 D and E are the fertile 

 st^uncns ; 1", 2", 3", 

 stigmas; 1" is modified to 

 form the ro.*tcHum, 



