62 



INTRODUCTION TO CYTOLOGY 



the interesting fact that the thallophyte groups with different predominat- 

 ing pigments are characterized by different principal products of metaboHc 

 activity. In the higher plants and the grass-green algse this product is 

 usually starch, in the yellow-green algse and diatoms it is oil, in the brown 

 algse it is pentosan, in the red algae (Floridese) it is Floridean starch, and 

 in the blue-green algae it is glycogen. 



Leucoplasts. — All colorless plastids, regardless of their size, function, 

 or relation to other types of plastids, are known as leucoplasts (Fig. 25). 

 They are found commonly in meristematic tissue and may be retained 



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e 



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f# 



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Fig. 25. — Leucoplasts in root cells, a-e, Yicia Faba; f, g, Pisum sativum; h, Hyacinthus 

 orientalis. The smaller bodies in b are chondriosomes. The light material in the enlarging 

 leucoplasts is starch. {After Bowen, 1929a.) 



in some kinds of differentiated cells, such as the glandular hairs of 

 Pelargonium. The leucoplast in Orchis is of a very fluid consistency, 

 undergoing amoeboid changes of shape and multiplying by irregular 

 fission (Kiister, 1911). In Polytoma uvella it forms a reticulum or series 

 of bands (Volkonsky, 1930). Many smaller leucoplasts represent juvenile 

 stages in the development of plastids of more highly differentiated types, 

 for under certain conditions they develop into the larger and more special- 

 ized leucoplasts known as amyloplasts (Fig. 28, C) and into the various 

 kinds of chromoplasts mentioned below. 



Chromoplasts. — Chromoplasts are plastids bearing one or more 

 pigments. They are frequently called "chromatophores, " but, since this 



