222 Plants and their Ways in South Africa 



contents may round off and form spores. The spores of 

 pond scums are preserved in the dried mud during the dry 

 months, and when the rains come they grow into new plants. 



In most algae a fusion of two cells forms a stage in their 

 life history. These may be like one another or an egg- and 

 sperm-cell may fuse which may be compared to the fusion in 

 higher plants. 



By means of chlorophyll, algae appropriate the CO2 dis- 

 solved in the water and so assimilate their own food. 



B. FUNGI. The fungi, which comprise the second class 

 of Thallophyta, differ from algae by the absence of chlorophyll. 

 This in itself would not justify a separate grouping of the 

 fungi, as this is not recognized as a basis for division in the 

 higher plants. The fungi, though they may be degenerate forms 

 of algae, are distinguished by their mode of developing and 

 their life history. 



Although as parasites the fungi are destructive to higher 

 plants their importance in the economy of Nature as sapro- 

 phytes and symbionts is only beginning to be understood. 

 Fungi grow symbiotically on the roots of many plants. By 

 removing the soil from the roots of a young oak plant the 

 threads (mycelium) of a fungus may be seen near their tips. 

 Reference is made on p. 342 to the fact that those growing as 

 mycorhiza on heath roots appropriate free nitrogen and are 

 thus of great importance to the soil. Some of the commonest 

 moulds as Penicillium (the blue mould) also appropriate free 

 nitrogen, as Miss Ternetz has found. 



The yeast plant Saccharomyces is of interest as being one 

 of the chief organisms concerned in alcoholic fermentation of 

 carbohydrates. When yeast cells are placed in starch paste or 

 in a solution of cane sugar an enzyme excreted by the yeast 

 sets up a digestive process. Starch uniting chemically with 

 water (by hydrolysis) becomes changed into maltose (C 12 H 22 O n ) 

 which by union with another molecule of water breaks up into 

 two molecules of glucose thus : 



C 12 H 22 O n + H 2 = 2(C 6 H 12 6 ). 

 Maltose Glucose 



