REDUCTION FOLLOWS DEPENDENCE 



239 



pcdium Selago expands its first leaves as green assimilating leaves, those 

 of L. clavatum are developed underground, and appear as minute colour- 

 less scales, succeeded later by green foliage leaves (Fig. 117). Again, in 

 Rotrychium virginianum the cotyledon is a green, expanded foliage leaf: 

 in B. Lunaria the first leaves are minute colourless scales. These cases 

 from among the Pteridophytes illustrate in two distinct series how, where 

 physiological dependence of the sporophyte is extended, owing to peculiar 

 circumstances, a local reduction of its vegetative system may follow. 

 They also have their interest for comparison with those Bryophytes which 

 have non-functional stomata, for in both the gametophyte appears to 

 have assumed increased responsibilities. Nevertheless, in these cases from 

 the Pteridophytes, the plant when ultimately 

 free shows no general reduction : the effect 

 is local, and does not extend to the mature 

 organism ; moreover, there is no reason to see 

 in such effects any reducing influence upon 

 the ultimate spore-output. 



Passing on to the independent sporophyte 

 as seen in the Pteridophyta after the embryonic 

 period is past, two cases require consideration : 

 the autotrophic types, on the one hand, and 

 on the other those sporophytes which show 

 indirect nutrition, such as is seen in the 

 mycorhizic types. In independent autotrophic, 

 homosporous Pteridophytes, the presumption, 

 as has been seen above, would be that they 

 would show evidences of amplification rather 

 than of reduction. So strong does this pre- 



Seedling of Lycopodinm clavatum, 



sumption appear that, wherever a line of (After Bmchmann.) xio. /-foot; 



i , r , a; = root ; bl= leaves here represented 



reduction IS Suggested for a homOSpOrOUS type, as minute underground scales. 



it should be incumbent upon its author to 



show physiological reasons why it should have occurred. Mere mor- 

 phological comparison without physiological support should be held as 

 an insufficient basis for theories of general reduction in homosporous 

 forms. 



But examples of special reduction, affecting parts or details of 

 homosporous Pteridophytes, are not uncommon. It seems not improbable 

 that the leaves of modern species of Equisetum are reduced as com- 

 pared with those of early Calamarian forms, and this may be held 

 as correlative to the development of the cortex in Equisetu?n as an 

 effective assimilating tissue. Certain of the leaves of Osmunda have an 

 arrested lamina, while the leaf-base remains as part of the protective 

 armour which covers the axis : potentially these are complete leaves, 

 and their arrest before maturity may be held as a case of reduction. 

 Such examples as these are in the nature of correlative adjustment of 



FIG. 117. 



