28 NATIVE BRITISH ORCHIDACEyE 



enabled the cultivation of orchids from seeds to be carried out on a large scale by 

 Charles worth and others. 



This living together of two organisms in 

 close association is termed symbiosis. A well- 

 known example of this is the lichen, which is 

 a composite plant formed of a fungus and an 

 alga in definite union. Germination of orchid 

 seeds without the aid of a fungus has now 

 been carried out successfully by Charlesworth 

 and Clement I in England, by G. andM. Ballion 

 in Belgium,^ and by M. Bultel in France,3 

 amongst others. Germination appears always 

 to be preceded by invasion by the fungus. In 

 Orchis, for instance, the embryo swells and 

 bursts its transparent covering, and forms the 

 protocorm or germ-tubercle, shaped like a 

 peg-top lying on its side (Text-figs. 4, II ; 5 , II 

 and 6, /, //). The pointed end (suspensor) 

 becomes invaded by the fungus, the infection 

 spreading on all sides (but not in the centre) 

 about half-way to the rounded end with its 

 little peg (incipient leaf). On the lower side of 

 the germ-tubercle rather long silky absorbent 

 hairs enter the soil. A central cylinder (stele) 

 begins to form (Text-fig. 6, //). The peg de 



. I. Protocorm of Orchis 

 New tuber appearing 



1+ 



2, 2<2. Later 

 Latter more 



5 . Protocorm shrivel- 



velops into a bud, B., but often only a single T^Jj^s-^^ 



leaf is formed during the first year. One or developed. 4. Roots appear. , 



1 1 ^1 U„^^..+r,o ling. 6. Plant early in third year. T. New tube 



two adventitious roots break tlUOUgh near tne ^^^a li^ie rhizome. 7. New tuber developed, the old 



An adult Orchis, about Septem- 

 already exists in bud. 



base (Text-fig. 6, 4, 6), the first root length- «- shrivelling^ ^^^^^_^^.^^ 



enine; downwards, contracting and drawmg 9. Next stage about January, in S. France. 10. 

 ° 111 ^^ ^-u ^;T TUo fi,-c«- About May or June, old tuber withered, new de- 



the germ-tubercle beneath the soil. The farst ^^^^^ ...pJoco^mofOrchism/Haris. B.Termi- 

 real tuber forms within the germ-tubercle, nai bud. sl Steie. 12. Protocorm of p/«to;/for^ 



j.Cd.1 Luuv^j. 1.VJ ■ 1 1 • fWoraH/fo, section in sprmg (after Bernard). 13. The 



below the bud, and emerges just beneath it same in May. p. Protocorm. Dotted area invaded by 



(Text-fig. 6, .,). At the end of the first year ^^^n,,;- .tS^sieT ^ "^""^^'^ '°^ 

 it becomes separated, together with the bud, 



from the germ-tubercle, being then hardly more than a few milUmetres long. In the 

 second or early third year it gives rise to a fresh tuber on a short stalk (Text- 



O.R. p. 560 (1924)- 



Revue hort. pp. 318, 334, 359 (1925)- 



Ibid. p. 103 (1928). 



