26 



NATIVE BRITISH ORCHIDACE^ 



V. THE LIFE OF AN ORCHID 



In 1838 Lindley wrote that nothing certain was known of the germination 

 of the Orchidace^. Seeds will not germinate under the ordinary conditions 

 of moisture, warmth, light and soil. Seedlings sometimes appeared in pots in 

 which the parent plant was growing, but when seeds were sown in such pots the 

 results were very uncertain. The seed of a grass consists mainly of a large store 

 of nutriment (albumen), and the embryo has 

 a radicle and plumule ready to develop into 

 a root and seed-leaf respectively on germina- 

 tion. The abundant albumen enables the 

 seedling to grow till it can fend for itself. 



The embryo of an orchid^ consists of a mass 

 of undifferentiated cells (Text-fig. 4, I). There 

 is no sign of rootlet or seed-leaf, and no albu- 

 men. The small oily food-content is used up 

 long before germination is completed.^ The 

 embryo cannot germinate without the aid of 

 certain species of fungus, the thread-Hke ^^^^ ^^ ^ ^ ^^^^ ^^ odontogioss.r. enclosing 



filaments (myCeUum) of wllich enter the seed the oval embryo. Sp. Suspensor. 11. Seedling of 



, ,1 ^.T-'^.r; .N„„J Odontoglossum. Sp. Suspensor through which the 



through the suspensor (J-^. iext-tlg. 4; and ^^^^ ^^^^^^ ^.^^ seedling. The filaments of the 



aid in the nutrition of the embryo. It has been f"">^""'^°^"^'^^'^^"r,'ii°^"f ^1^^^ w 



-' . . and are passing out through the root-hairs (r.*.; on 



found that germination results from invasion the left-hand side. The filaments in the upper ceUs 



1 ^ r ^ r> 7 ■ J. ■ -h .„ „.- ^i-1,^.- ^llJor^ are less distinct, being in process of digestion by the 



by the fungus VJoi^OCtoma repens or other aliied ^^y^ From Noel Bernard's "fitudessur la tuberisa- 



SOecieS M. Beau3 made the following experi- tion", Kwuegmirale de Bota«iq«e, xw (1902), by kind 

 r r 1 J permission of the editor. 



ment. A watchglass, convex face downwards, 



was placed on gelose (vegetable jelly), and mycelium on the latter, when its fila- 

 ments rapidly cHmbed over the glass. Seeds were then sown on the myceUum, so 

 that they had no contact with the gelose. The mycelium penetrated into the embryos 

 which germinated normally. If the filaments were destroyed growth stopped. They 

 evidently conveyed nutritive matter from the gelose to the embryo. 



When thus invaded by the endophyte (a plant growing within a living plant), the 

 embrj^o swells into a protocorm (Text-fig. 5, 11), a greenish or whitish tubercle 

 hardly visible to the naked eye, with a small peg on the top, the rudiment of the 

 first leaf. Numerous absorptive hairs {r.h. Text-fig. 4, H) are produced at the base 



1 Rendle, Classification of Flowering Plants, ed. i, Monocoty. pp. 346-9- 



2 Clement, O.R. p. 560 (1924). „^ , ■ 1 - „ /^ i, ., r r s 



3 Beau (aovis),"Surle role trophiquedesendophytesd'Orchidees [C.K.Ac.Sc. i920,p.675). 



