3 
The Evolution of Plants. 
quotation from the “ Grundziige.” But it should be noted that 
while this ignorance of the rich and marvellous vegetation of the sea 
by the “ land botanist ” may explain the absence of any serious 
attempt to go to seaweeds for light on the evolution of land plants, 
it has nothing to do with “ antithetic ”as opposed to “ homologous ” 
alternation. The author ignores Pringsheim (1856, etc.) 
The second thesis is that there is no probability of plant life 
having migrated from the sea to the land, via estuaries and rivers 
to freshwater swamps, and that the origin of land plants from 
marine forms took place by what the author calls transmigration? 
i.e. the slow emergence of land from the sea, carrying with it a 
plant population. The migration via inland waters the author 
thinks impossible because of the deficient food supply in the form 
of salts, and he points out that all freshwater algal vegetation is 
in fact diminutive in size (starved and stunted) as compared with 
that of the sea. The diminished food-supply of such habitats would 
lead to a serious diminution in output of reproductive cells and hence 
in failure to compensate the wastage of the race, and to ultimate 
extinction. Only inferior (unicellular and filamentous) forms could 
survive under such conditions, and we must look for the ancestors of 
the main land vegetation among massive forms comparable with the 
best equipped modern seaweeds. 
In considering the possibility of the transformation of a 
massive seaweed into a land plant we have first to envisage the 
actual change of conditions involved, in their effect on the 
vegetative economy, the day-to-day life of the plant. First 
of course we have the localisation of water supply and of the 
supply of the essential elements of the “ food salts.” Of these the 
second is by far the most insistent, since the author calculates that 
over 150 litres of sea water would have to be passed through the 
plant in order to obtain sufficient nitrogen to make one gram of 
aqueous plasma (taking the nitrogen content of the sea—the 
original nutritive medium—as one part in ten million). This 
proportion of water to combined nitrogen, however, is progressively 
decreased as we pass to soils containing more humus. “ A 
progressively sub-saturated atmosphere with attendant desiccation, 
now appears as a blessing in disguise,” as enabling the plant to get 
rid of this enormous quantity of excess water, at the same time 
stimulating the flow of the current. Meanwhile increased 
insolation, and increased facility of gaseous exchange, immensely 
1 The fitness of this word to express the hypothetical phenomenon in 
question is not very clear. 
