20 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



Physiologically, mitochondria are' organs of elaboration. In 

 them, through some unknown physico-chemical phenomena, most of 

 the products of cell activity may be formed. The product, whatever 

 may be its specific nature, has its origin in a granular mitochondrium 

 or in a rod-mitochondrium. Each product is surrounded by a 

 mitochondrial exterior surface inside of which it develops slowly; the 

 exterior surface remains until the product has reached its state of 

 maturity. 



It has been known for some time that there exist in higher plants 

 corpuscular elements called plastids or leucoplastids, which also possess 

 a synthetic function. Some, the chloro plastids, make the chlorophyl 





A 



FIG. 10. Formation of chloroplasts in the young leaf of barley. A, Very young 

 cells in which appear rod-mitochondria. B, Older cells in which the rod-mitochondria 

 are transforming themselves into chloroplasts. C, Cells in which the chloroplasts 

 are definitely constituted. 



which, by using rays of light as energy, forms starch; others, the 

 amylo plastids, confine themselves to forming starch from the excess 

 sugars found in the cells; still others, the chromo plastids, constitute the 

 pigment bodies of plants (xanthophyl, carotins). It has been recently 

 shown that plastids are nothing but- mitochondria which have under- 

 gone greater differentiation and specialization than those which, at the 

 expense of ordinary mitochrondria derived from the egg, have increased 

 in size (Figs. 10, n). 



Mitochondria have been found in most protozoa and fungi. In the 

 latter they take part in the formation of reserve products, especially 

 the metachromatic corpuscles of which more will be said later. 



Mitochondria are most highly developed in algae where they give 

 origin to chloroplastids as in higher plants, On the other hand, in 



