MITOCHONDRIA IN PLANT AND ANIMAL CELLS. 211 



But this is only a single isolated instance and many facts of 

 interest can be brought to light by a broad general discussion 

 of mitochondria in many forms which I shall now venture to 

 make, based in part upon the literature. 



DISCUSSION. 

 Distribution. 



In plants mitochondria have been recorded from the Angio- 

 sperms to the Fungi; but it is difficult or even impossible to 

 demonstrate their existence in the very lowest forms of plant 

 life, like the Myxomycetes , the Schizomycetes and some of the 

 Alga; though in these groups structures of questionable nature 

 have been discovered which may ultimately prove to be mito- 

 chondrial. This absence of typical mitochondria in the lowest 

 plants may be contrasted with their almost universal occurrence 

 in the Protozoa. In all forms of animals, from amoeba to man, 

 which have been investigated with adequate methods of tech- 

 nique, they occur without exception. 



With regard to the different types of cells. In plants, they 

 occur from the tip of the root to the end of the stem, wherever 

 the protoplasm is active, with but few exceptions. The same is 

 true in the various categories of animal cells. They are met 

 with in gland cells, nerve cells and muscle cells; in connective 

 tissue cells, germ cells and almost all others,, except in the 

 terminal stages of cytomorphosis. And this is one of the greatest 

 points of similarity between these granulations in the plant and 

 animal kingdoms, that it to say their progressive diminution 

 and final absence in the later stages in the life of the cell. 



I refer, for instance, to the decrease in number of mitochondria 

 in plant cells, which runs parallel to the formation of chloroplasts, 

 for it is said (Guilliermond, '12, plates 17-18) that when the 

 plasts are fully mature few if any mitochondria remain (which 

 reminds one of the single large chloroplast and the absence of 

 mitochondria in some algae) ; and these are mature and highly 

 differentiated cells. In animals there is a similar disappearance 

 of mitochondria in the life cycle of red blood cePs. In the young, 

 nucleated forms they are very abundant, they become less and 

 less so as the cell differentiates; a few persist aft ^r the nucleus is 



