HOW PLANTS SPREAD AND MULTIPLY 39 
the good farmer’s neighbours, who considered that local 
patriotism might perhaps be carried a little too far. 
This vegetative reproduction has, however, serious dis- 
advantages when compared with competition by means 
of seeds and spores. The disadvantages are three: it 
cannot compete in numbers as a rule; the complete 
plants are not so hardy as seeds; and they are never 
likely to travel so far, unless, like the seaweeds or the 
pondweeds, they have got currents of water to help them. 
As to the numbers, the figures given at the beginning 
of the chapter should satisfy you on that point. The 
hardiness of the spores and seeds deserves a word or two. 
Wrapped up as they generally are in a coat, or husk, they 
are not so much troubled by changes of temperature. The 
spores of funguses, for instance, ignore a degree of heat 
that would kill their parents at once, and the breath of 
frost that would devastate a wheat field would have no 
effect whatever on the unsprouted children. Some strik- 
ing experiments in the same direction were tried by 
Professor Dewar, who tested the effect of extremes of 
cold upon such common seeds as peas, cucumber, and 
vegetable marrow. He immersed them for six hours in 
liquid hydrogen. Now hydrogen is an extremely volatile 
gas, and does not liquefy until it has been brought to 
a temperature two or three hundred degrees below the 
freezing point of water. A pea or cucumber plant, put 
into a block of ice, would speedily die, but these seeds, 
though in a far colder place, came out at the end of six 
hours as bright and clean as when they went in, and 
actually all of them, when put in the earth, grew up into 
plants! Seeds have also the capacity to lie dormant for 
a considerable time, starting into active life only when 
they find themselves in a suitable position. Actual ex- 
