580 TRANSACTIONS OF SECTION K. 
changes or ‘ mutations,’ which are given off in new directions and are inherited ; 
they are distinguished from fluctuating or individual variability in which the 
variations are merely of a plus or minus character and are not inherited. The 
mutation gives rise to a new inheritable specific character, and is the source of 
the so-called elementary species. A comparison of these elementary species 
(e.g., Jordan’s Drabas) shows that their distinguishing features are precisely 
those which characterise fluctuating variability—relative size and degree of 
development of parts, hairiness, time of flowering, &c. Each species represents 
the resultant of a number of slight individual variations of already existing 
characters, and suggests some process of selection of a number of slight in- 
dividual variations rather than a sudden mutation. A similar remark applies to 
the cases of seasonal dimorphism in alpine meadows described by Wettstein. 
Sports or mutations arising under cultivation are of a different character, 
being generally marked by some one striking character such as cutting of the 
leaf, monophylly in species with compound leaves, &c. Generally speaking, such 
would not persist in Nature, especially where the floral organs were affected, as 
marked changes in these would be detrimental. These afford no evidence as to 
the origin of species in Nature. 
Recently Lotsy has suggested crossing as the source of new species. Pre- 
sumed stable genotypes or elementary species give rise when crossed to unstable 
heterozygotes which segregate into a new series of genotypes. There is no sug- 
gestion that the new batch of species is more in accord with environment than 
the parents, and there seems no reason for their persistence. In place of slight 
variations of well-adapted organisms this theory suggests for the operations of 
Natural Selection an indiscriminate series of new forms. Is there evidence for 
the occurrence of these hybrids or of these series of aberrant and largely 
monstrous forms in Nature in sufficient quantity to account for the origin of 
new species? Direct action of the environment an important factor in the 
origin of species. ; 
2. The Climate in Northern Temperate and Arctic Zones during the 
Latest Pleistocene Age. By Professor GuNNAR ANDERSSON. 
3. The Geographical Distribution of the Sea-grasses. 
By Dr. C. H. OstENFExp. 
4. The Fossil Plants discovered by Captain Scott’s last Hapedition in 
the Antarctic Regions. By Professor A. C. Smwarp, I.R.S. 
WEDNESDAY, AUGUST 19. 
The following Papers were read :— 
1. Relationship of Fungus and Alga in the Lichen-thallus. 
By Miss A. Lorrain Suir. 
General account of lichens and description of the composite thallus. Early 
theories and speculations recalled as to the nature of the different tissues, more 
particularly in the gelatinous lichens. The,green cells determined by Wallroth 
to be brood-cells or ‘ gonidia,’ a theory which was accepted for many years. 
Resemblance of the gonidia to free-growing aerial alge more and more realised. 
Metamorphosis of the alga Nostoc to the lichen Collema finally observed by 
Stahl, who also likened the colourless filaments of the thallus to fungal hyphe. 
An account of the culture experiments by which the alga was successfully 
isolated from the thallus by Speerschneider and observed by him to grow inde- 
pendently and to increase by division. Following the same methods, Famintzin 
and Baranetsky obtained the formation of zoospores in free-growing gonidia. 
