THE LICHEX AS TRANSMIGRANT 41 



to consider the possibility of the deterioration of the photosynthetie 

 surface-layers of a seaweed-soma of comparatively high grade, 

 equivalent, that is to say, to a type of plant with a reproductive 

 organization as efficient as that of the modern Florideae. 



Only a very slight acquaintance with the somatic mechanism of 

 seaweeds is sufficient to indicate the manner in which this may be 

 done. For example, in an ordinary Fucoid the photosynthetie units, 

 which carry out the constructive metabolism of the plant in imme- 

 diate association with the external food-solution, constitute but 

 a relatively thin brown film, about 100 /x deep, over the more massive 

 mechanical tissues of the interior ; the peripheral more active units 

 being 10-15 fi only. Stripped of these outer layers, the whole plant 

 reduces to a system of hyphal strands, as an interwoven mechanical 

 tissue of ' descending hyphae,' to all intents and purposes the mycelium 

 of a Fungus-axis. The same effect is more readily produced in a 

 Laminarian (cf. L.jJexicaulis), if kept in standing water for a day or 

 two ; though in such a type the central tissues are less hyphal, and 

 may even present a massive growth of mechanical tissue with annual 

 increments as ring-effects (i. Cloustoni). A little consideration 

 shows what happens. The actively metabolic surface-layers, accus- 

 tomed to the free interchange of gases and food-salts with the external 

 medium, are more sensitive to changes in the environment as they are 

 the more superficial and the more actively sj^nthetic. In standing 

 water, soon deprived of all free oxygen, they die immediately in the 

 dark owing to lack of oxygen for aerobic respiration ; and in the 

 light they also soon fail for lack of further supply of the essential 

 food-ions. On the other hand, the more internal tissues, previously 

 wholly heterotrophic at the expense of the surface-layers, and existing 

 with a minimum oxygen-supply oidy available by diffusion from the 

 periphery, are on a wholly different footing. Conditions that involve 

 rapid death to the autotrophic surface-cells do not necessarily injure 

 the internal mechanical and reserve tissues. This roughly visualizes 

 the origin of the heterotrophic ' Fungus ' from residual vegetation of 

 the sea, banked in standing water, or shaded under decaying masses 

 of vegetation. A 'Fungus' is to be regarded, not as a new land- 

 growth, evolved de novo by the progressive elaboration of a mere 

 weft of filamentous mycelium [however much some filamentous alga3 

 may have similarly given rise to filamentous phyla of Fungi (cf. 

 Mucorini)\ ; but a higher Fungus of the land is in short a ' skinned 

 seaweed,' implying a more or less elaborated algal growth -form, in 

 which, on the death and decay of the older metabolic and autotrophic 

 surface-layers, the exposed internal heterotrophic tissues continue 

 their heterotrophic (and even conceivably anaerobiotic) existence at 

 the expense of the soluble carbohydrates of the standing and non- 

 aerated medium. The normal progression of heterotroprrv in the 

 transmigrant fungus-phyla, following the natural consequences of a 

 residual marine environment of plant-rejectamenta, thus sufficiently 

 accounts for the loss of the cortical and photosynthetie tissues, as 

 also for the destruction of the protective ' cuticle ' and tissues pre- 

 viously resisting intrusion. The two things go together, and need no 

 longer excite surprise. The massive organization of a Fungus, with 



