20 SOUTH AFRICAN BOTANY 
present are mineral salts, carbohydrates, fats, and some- 
times ferments and alkaloids. 
11. The Nucleus.—The nucleus is the most important 
part of the protoplasm. It usually has a reticulate 
structure, and consists of a number of threads in which 
lie embedded a number of granules. One or more 
denser bodies called NucLEOLI are present in the network 
of threads, and the nucleus itself is surrounded by a thin 
membrane. It is usually spherical in shape, but in 
older or elongated cells it becomes flattened and elon- 
gated. It plays a most important part in cell division, 
splitting up into a number of filamentous bodies called 
CHROMOSOMES, each of which splits into halves longi- 
tudinally, the separate halves forming two new nuclei. 
Tn other processes the nucleus divides into two fragments. 
In either case division of the nucleus always precedes 
division of the cell. 
12. Plastids.x—These bodies may develop in various 
ways. .If they turn green they are CHLOROPLASTS or 
CHLOROPHYLL corpuscles. If red or yellow, asin petals 
or fruits, they are termed CuHromopuasts. If they 
remain colourless they are termed LEUCOPLASTS or 
starch-forming corpuscles. The chloroplasts hold the 
green colouring matter of plants—CHLOROPHYLL—in 
solution. This chlorophyll is soluble in alcohol, ether, 
paraffin, oils and carbon bisulphide, and, consequently, 
a solution in alcohol can be obtained by steeping killed 
leaves in alcohol for a short time. Other pigments 
may be associated with the chlorophyll—yellow, blue, 
or red. Chlorophyll is only developed in the chloro- 
plasts under the influence of light. Before leaf-fall 
occurs the chloroplasts undergo disorganization, and 
