FUNGI. INTRODUCTORY 403 



reliable record. In the Lower Devonian, long before there were 

 any Flowering Plants, there is abundant evidence of Fungal structure 

 existing under conditions favourable to that habit. It does not, 

 however, follow that all organisms which adopted a " fungal " habit 

 early were allied to one another, nor that all Fungi originated at 

 the same time. The existence of parasitic and saprophytic Seed- 

 Plants is a warning against such an assumption. We should rather 

 be prepared to recognise that " Fungi " have originated along more 

 than one line of Descent, and probably at different times, from very 

 early periods onwards. It is natural to seek for some Algal origin 

 for them, for in many features they resemble Algae. At least two 

 general sources can be suggested, though the actual points of connec- 

 tion by descent may have been numerous. One is from non-septate 

 Algae, such as the Siphoneae. This has probably given rise to those 

 non-septate Fungi, which are called Phycomycetes, from their Alga-like 

 features. The other is from septate Algae ; and there are various 

 grounds for believing that the septate filamentous Red Algae gave 

 rise to many at least of those septate Fungi, which are called the 

 Eumycetes. 



The lower organisms, and especially those of aquatic life, are habitually 

 in close juxtaposition. As a rule any large Seaweed or submerged fresh-water 

 plant bears innumerable smaller organisms attached to its surface. Sometimes 

 they penetrate into its tissues. Some by preference frequent certain hosts. 

 Thus Polysiphonia fastigiata is regularly borne on the Brown Tangle Asco- 

 phyllum nodosunt, and its filaments extend deeply into its tissues. The proof 

 of actual parasitism is here incomplete, though the regularity of occurrence 

 arouses suspicion. But there can be no doubt of the physiological dependence 

 in Harveyella mirabilis, which grows as a colourless parasite penetrating 

 the tissue of Rhodomela, one* of the Red Algae (Fig. 339). The parasite is 

 by structure and propagative organs clearly another Red Alga, which acts 

 like a true Fungus. Among the Green Algae, Coleochaete, one of the Ulothri- 

 cales, grows habitually on the surface of submerged plants. The allied 

 Mycoidea parasitica, though still green, penetrates the tissues of the leaves 

 of Camellia. Other similar cases might be quoted from allied septate Algae. 

 Again, the green Siphonaceous Phyllosiphon lives habitually in the intercellular 

 spaces of the leaf of Arisarum, causing discoloured patches. Such examples, 

 which might be greatly extended, show how juxtaposition may give opportunity 

 for parasitic encroachment. They are seen in modern living forms referable 

 to recognised groups of Algae. They suggest how in the past fungal parasitism 

 may have arisen. They also prove that the " Fungal " condition may be 

 arising now, as in the past, and along a plurality of evolutionary lines. 



The Fungi are very various in habit, and in form. The most 

 familiar types are the large Mushrooms and Toadstools, or " seats 

 of death," so called in allusion to their trequently poisonous character. 



