MYCORHIZA AND REDUCTION 241 



the Pteridophytes, leads to a general reduction of the infected sporophyte 

 as a whole. 



The particular family in which the argument relating to mycorhiza has 

 been specially applied is the Ophioglossaceae. A more detailed account 

 of it will be given where the family is specially described below; but 

 meanwhile it is to be noted that there is throughout the Adder's Tongues 

 a close parallelism of proportion of the sterile lamina to the fertile spike : 

 this is indeed one of the most remarkable features in the morphology of 

 the family, the parallelism extending not only to the size of the respective 

 parts, but also to the character and extent of the branching of each. If 

 saprophytic nourishment by the mycorhiza were in this case a real 

 substitute for chlorophyll-assimilation the sterile lamina would fall behind 

 the spike in its dimensions ; but in the normal representatives of the 

 family it does not. The conclusion follows that in the mature sporophyte 

 of the Ophioglossaceae the mycorhiza is not functionally an effective 

 substitute for nutrition by chlorophyll-assimilation. 



There is, however, one series of species in that family in which the 

 proportion of the two parts is not maintained, viz., the section Ophioderma 

 of the genus Ophioglossum. Here the epiphytic O. pendulum shows 

 approximately the usual balance ; but in O. intermedium, a land-growing 

 species, the sterile lamina is relatively small, while in O. simplex, also a 

 ground-growing species in which mycorhiza is present, the lamina appears 

 to be altogether unrepresented. I regard this section, Ophioderma, as a 

 series in which mycorhiza has become effective as a substitute for chlorophyll- 

 nutrition, and that reduction of the vegetative system has actually followed 

 as a consequence : nevertheless the spike, being effectively nourished, 

 retains its dimensions. But disturbance of the balance of the vegetative 

 and reproductive systems such as this is a very different thing from any 

 general reduction of both, such as is sometimes assumed to follow in 

 consequence of a symbiotic habit. 1 



Another family which provides an interesting parallel in this respect to 

 these Ophioglossaceae is that of the Psilotaceae. In Tmesipteris there is a 

 reasonable balance of size between the forked sporophyll and the bilocular 

 synangium. In Psilotum this balance is not maintained, for the small 

 sporophylls are ineffective as assimilating organs while the trilocular 

 synangium is still of large size. It is true the green axis is an effective 

 organ of assimilation, but it would appear probable that the mycorhizic 

 state also assists. 



The discussion of the parts played respectively by amplification and 

 reduction in the genesis of the homosporous sporophyte may now be 

 summed up. The end of its development is the production of the 

 largest number of effective germs. To increase their number involves 

 amplification of the propagative system. This involves also in many 

 cases amplification of the nutritive system. However, this is not an 



1 See Scutt, Studies, p. 511. 

 Q 



