fuller] HOIV ORCHID SEEDS GROW 23 



thing like mould. Such fungi usually cause disease, but in the 

 orchid they seem necessan,' for the life of the plant. In the 

 varieties in which they are most abundant the roots are short 

 and stout instead of being long and fibrous. This is particularly 

 true of orchids growing as epiphytes, although it is not uncom- 

 mon in our soil orchids. It would seem that the fungus and 

 the orchids have lived together so long that a condition of mutual 

 benefit and mutual dependence has developed. 



Usually when seeds are properly moistened they require only 

 the proper temperature and a supply of oxygen for respiration 

 and they will germinate, but most orchid seeds need something 

 more, and that is the fungus that grows within their roots. 

 Sometimes this is present in the soil near the parent orchid, but 

 at other times it seems necessary to sow the seeds in contact 

 with the orchid roots. This French botanist isolated the fungus 

 and grew it upon a jelly made from the orchid roots. He then 

 planted his orchid seed. Some of the fungus was put alongside 

 of part of the seed, and only those seeds furnished with fungi 

 grew. First they swelled to many times their size and then de- 

 veloped a bud. leaves and root. The other seeds swelled to 

 about twice their size and then remained unchanged for two years 

 or until they decayed. 



It is now possible to divide the orchids into three classes, 

 according to their germination habits. The first class contains 

 a few soil-growing orchids, whose seeds germinate in the usual 

 manner but rather slowly. Then comes a large class whose 

 seeds sometimes germinate without fungi, but that germinate 

 more rapidly and attain a more vigorous development if these 

 organisms are present. Finally there are many orchids whose 

 seeds have entirely lost the power of independent growth and 

 are entirely dependent upon the stimulus supplied by infesting 

 fungi. The parasite has apparently quite ceased to be harmful 

 and has become necessary for the health and for the very life 

 of the orchid. Such close partnerships are seldom found in 

 nature. 



