CHAP, i.] PLANT ARCHITECTURE. 35 



organs of locomotion and enable the antherozoid to swim 

 in water. Even when inclosed within a rigid cell-wall, 

 the protoplasm not unfrequently exhibits well-marked 

 movements, the whole of the peripheral layer of proto- 

 plasm moving round the cell (rotation), or currents that 

 carry along minute granules and move in its substance. 



Cell- contents. In addition to the protoplasm, which 

 itself constitutes the cell, a considerable number of sub- 

 stances are met with in cells, the presence of these sub- 

 stances being determined by the position occupied by a 

 given cell in the general structure of the plant. The 

 following are the most important of cell-contents : 



(1) Chlorophyll, or the green colouring matter pre- 

 sent in the superficial cells of plants. Light, being an 

 indispensable factor in the formation of chlorophyll, it 

 is consequently absent from the internal parts of plants, 

 and also from underground portions, but in the latter 

 case it can be shown that the absence of light is the 

 cause of the absence of chlorophyll, as when the under- 

 ground portion is exposed to light it often becomes 

 green, as seen in potatoes that have been exposed to 

 light during growth. In the majority of plants the 

 chlorophyll consists of minute particles called chlorophyll- 

 grains that are imbedded in the protoplasm, but in some 

 of the simpler Algae the chlorophyll is diffused as a 

 liquid throughout the protoplasm. The almost universal 

 green colour of the vegetable kingdom is due to the 

 presence of chlorophyll in the superficial cells. Its 

 important functions will be dealt with at a later stage. 



(2) Starch first makes its appearance as a solid organic 

 product within the chlorophyll grains, and continues to 

 accumulate so long as the chlorophyll is exposed to 



