Plants and their Ways in South Africa 



blossom and die, where none but their Maker beholds their 

 beauty. Plants are found, beautifully white and delicate, deep 

 down in the darkest mines. They are able to withstand the 

 heat of boiling springs, and e.xplorers from the frozen Antarctic 

 return with mosses and lichens. Germs of plants kept in 

 liquid air for six months at a temperature of — 190° C. have suf- 

 fered no injury, while others have remained for ten hours in a 

 bath of liquid hydrogen, 60° colder still, and have then come 

 forth and flourished.' Plants are quite at home on cheese and 



canned fruit, and an old shoe 

 cast upon a rubbish-heap 

 may boast its botanic garden. 

 These are the moulds, and 

 against them the housekeeper 

 is waging constant warfare. 



Some plants are so small 

 that the sharpest eyes cannot 

 see them without powerlul 

 microscopes. Of these, some 

 grow in the human body 

 better than anywhere else. 

 We call them germs. Sev- 

 eral kinds grow on the teeth 

 and cause their decay, un- 

 less the teeth are carefully 

 brushed. One kind, which 

 passes part of its life in im- 

 pure milk or water, lodges in the throat and causes diphtheria ; 

 and another produces enteric fever, so that eternal vigilance is 

 the price of health. 



' To liquefy air require.s intense cold. The temperature at which a 

 gas liquefies is called its critical temperature. Hydrogen requires the 

 lowest temperature ot any gas yet liquefied. The particular pressure 

 under which a gas liquefies when reduced to its critical temperature is 

 known as its critical pressure. Thus, hydrogen gas liquefies at- 23S C. 

 (the critical temperature) under a pressure of 15-3 atmospheres. The 

 critical pressure of o.xygen is 58 atmospheres at a critical temperature of 

 - TiS-S^. At temperatures below the critical temperature a gas liquefies 

 under less pressure. 



Fig. 1. — Common mould {.]///r,>r >////- 

 cede) : I. An entire plant with six 

 sporangia in different stages of rle- 

 velopnient (strongl}- niagnitied). II. 

 .Single sporangium with spores /' ( x 

 200). (From Thome and Bennett's 

 ''Structural and Physiological Bo- 

 tany ".) 



