172 M. C. COOKE ON THE DUAL-LICHEN HYPOTHESIS. 



Are Lichens Autonomous Plants ? Is it, or is it not, possible 

 from the structure or the development of a plant to predicate with 

 tolerable certainty whether that plant is within itself a perfect or 

 complete plant or not ? If we sow a seed under favourable con- 

 ditions, preserving it from all external influences, and that seed 

 germinates, produces a root, a stem, ultimately leaves, the flowers, 

 with stamens and pistil, then in course of time, as the ovary 

 matures, seed in all respects identical with that from which the 

 plant originally developed ; in such a case we should certainly 

 conclude that the plant under examination is a complete and perfect 

 plant, possessed of all the essentials for the reproduction of its 

 species. 



If, instead of following the plant through all its stages, we bring 

 experience to our aid in judging of probabilities, we examine a plant 

 possessed of root, stem, leaves, and complete reproductive organs, 

 bearing perfect seeds, we may safely conclude that we are examin- 

 ing a complete and perfect plant. All these organs we know by 

 experience are not essential to the perfection of fruit in all plants. 

 In some the stem will be almost obsolete, as in the daisy, or without 

 true leaves, but with leaves and stem fused into a foliaceous expan- 

 sion, as in the duckweed ; and yet there will be no suspicion that the 

 plant is incapable of reproducing its species, thus proving itself a 

 perfect plant (using the term perfect, as in the sense of complete- 

 ness). Hence we may conclude that if a plant is capable of repro- 

 ducing its species, when excluded from all external influences, by 

 means of its own proper organs, we may assume such an one to be a 

 complete plant, whatever modifications in structure may be present, 

 and whatever secondary organs may be absent. Such plants, how- 

 ever minute or simple in structure, are entitled to rank as autono- 

 mous plants. 



The spores of a species of Peziza germinate, producing root-like 

 fibrils of great delicacy, and upon these arise small globose bodies 

 which, as they grow, become perforated at the apex, ultimately 

 expanding into a cup, which completes the vegetation of the little 

 plant. It is simply a minute fleshy cup, with a fibrous base, by 

 means of which it is attached to the matrix. A section of this 

 cup exhibits the reproductive bodies, the ova (if such a term may 

 be permitted) contained in elongated tubes, closed at the apex, and 

 packed side by side. These spores, when matured, are capable of 

 reproducing the form and character of the parent. Yet simple as 



