114 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



Lewitsky (1910, p. 542) and Pensa (1910, p. 325) deserve credit for opening 

 up this important field almost simultaneously. Lewitsky studied mitochondria 

 in growing asparagus tips. He claims to have discovered that the leucoplasts arise 

 from them, and advances the general conclusion that the chondriosomes (mito- 

 chondria) in plant cells are to be regarded as formative granules, just as they are 

 supposed to be in animal tissues. In other words, he extends Meves's important 

 generalization ip. 101) to plant tissues. Pensa arrived at essentially similar results, 

 and the problem has since been flooded with contributions from all quarters. 



We have to consider the formation of leucoplasts and starch; of chloroplasts 

 and chlorophyll; of chromoplasts and pigments of almost infinite varietj^; and of 

 the elaioplasts, which elaborate fats. Let us analyze the facts observed and see 

 whether they permit of any other interpretation than that of direct chemical trans- 

 formation. It can not be denied that there is a very definite topographical rela- 

 tion between the mitochondria and the deposition of these substances, for they 

 are actually laid down within them, but it is too much to say that we are here deal- 

 ing with an actual chemical transformation of the mitochondrial substance. Yet 

 this is just the claim that Guilliermond (1912r(, p. 394) makes. He has shown that 

 filaments which possess these swellings are chemically different from the other mito- 

 chondria in the cell, because their solubilities in certain fixatives are different ; but 

 it does not follow, nor is there any reason to suppose, that further alterations occur 

 in the constitution of the mitochondria by which they become changed into starch, 

 pigments, chlorojihyll, and so on. Guilliermond (1912^, p. 408) points out at length 

 that Hoppe Seyler and others look upon chlorophyll as toeing a combination of 

 lecithin and other substances, and that it accordingly resembles mitochondria 

 quite closely. The other pigments and the crystalline substance "carotine" differ 

 widely from mitochondria chemicall}-. To my mind, the facts observed, which no 

 one would question, demonstrate nothing more than that the said topographical 

 relationship between mitochondria and the formation of these materials exists. 

 These substances are simply dejiosited. or accumulated, or heaped up within the 

 mitochondria, which serve as a convenient and suitable vehicle, by virtue of their 

 chemical and physical properties. There is good reason to believe that some of 

 the substances, like the pigments, may be soluble within them. They may also 

 act as condensers, as Regaud believes. But what I want to make absolutely clear 

 is that this does not necessarily involve any chemical change whatever in their 

 constitution. 



The fact that mitochondria diminish in number, pari patisu, with differentiation 

 in plant cells as well as in animal cells, does not mean that they change chemically 

 into the products of differentiation, as some investigators have tacitly assumed, 

 for this decrease in amount of mitochondria is probably associated with a decrease 

 in the rate of metabolism which we know occurs with differentiation and senility. 

 The evidence now at hand that the mitochondria are concerned with metabolism 

 is given in detail on page 131. There is nothing to indicate that the mitochondrial 

 substance about the granule of starch, or the i:)igment, as the case may be, is chem- 

 ically transformed into something else as it decreases in amount. It may simply 



