240 AMPLIFICATION AND REDUCTION 



parts of the shoot, inter se, and cannot be held to be examples of general 

 reduction. 



There remain to be considered those sporophytes which show some 

 form of indirect nutrition, the commonest of which is the mycorhizic 

 symbiosis. The occurrence of a symbiotic state is often loosely held 

 to be equivalent in itself to a demonstration that the organism in which 

 it occurs has been the subject of general reduction ; and reference is apt 

 to be made in support of this to extreme cases, where it has in fact led 

 to complete saprophytism. But it is necessary to be clear what effects 

 they are which necessarily follow upon this habit, as apart from those 

 which are occasional and extreme : for it is only the former which can 

 properly be counted on for argument. Stahl has indicated that the usual 

 structural concomitants of mycorhiza in green plants are such as lead 

 to economy of the water-interchange : l viz., a restricted root-development, 

 with thick unbranched roots, and absence of root-hairs : little structural 

 provision for water- transfer and an absence of organs of water-secretion ; 

 while a leathery texture of the leaf, a feature of other plants which 

 economise water, is not uncommon. But these characters are by no 

 means uniformly or exclusively found in mycorhizic plants : for instance 

 Cyathea is mycorhizic, but it shows such characters as the leathery leaf 

 less obviously than Aspletiium nidus and Osmunda regalis, which are not. 

 When present the features above named may be held to be indicative of 

 a probable reduction in respect of the parts immediately affected ; but 

 that is a very different thing from the general reduction which is some- 

 times assumed to follow mycorhiza as a necessary consequence. General 

 reduction implies an effect on both the nutritive system and the propagative 

 system. But it is to be clearly understood that so far as the mycorhizic 

 habit affects nutrition, by yielding as it does in some cases an efficient 

 saprophytic supply,- the reduction will appear in the vegetative system 

 only, and not in the propagative. This is amply illustrated in Phanero- 

 gamic plants such as Neottia and Sarcodes? where the flowers and fruits 

 remain of the usual types though the vegetative system is reduced. 

 Similarly, among Pteridophytes, if mycorhiza were really effective in them 

 as a considerable means of saprophytic nourishment, we should expect the 

 consequent reduction to appear in the vegetative system, with a loss of 

 chlorophyll in extreme cases ; but that the spore-producing parts should 

 remain of the usual dimensions and character of the family : that is, 

 supposing the saprophytic supply to be as efficient as the normal chloro- 

 phyll nutrition. Now, putting aside certain exceptions to be noted below, 

 such a condition is unknown among Pteridophytes, and its absence goes far 

 to show that the mycorhizic symbiosis seen in them is not a fully effective 

 source of organic nutritive supply. The facts do not bear out the 

 general assumption that mycorhizic symbiosis, as seen in certain of 



1 Pringsh. Jahrb., xxxiv. , p. 539. 



2 See F. W. Oliver, on Sarcodes, Ann. of Dot., iv. 



