144 CHEMISTRY OF PLANT LIFE 



PLANT CEREBROSIDES 



Bodies similar to the animal cerebrosides seem to occur in 

 many plant tissues, since plant lipoids which yield no phosphorus 

 when hydrolyzed have often been isolated. The sugar which con- 

 stitutes the alcoholic portion of their structure appears to be 

 galactose in every case which has been reported. Beyond this, 

 little is known of the structure of these plant cerebrosides, as they 

 are very difficult to prepare in pure form and not easily hydrolyzed. 



PHYSIOLOGICAL USES OF LIPOIDS 



Lipoids are so universally present in plant and animal tissues 

 and so commonly found in those parts of the organism in which 

 vital phenomena are most pronounced (brain, heart, embryo of 

 egg, embryo of seeds, etc.), that it is evident that they must play 

 some important role in the activity of living protoplasm. There 

 is, as yet, however, no definite and certain knowledge of what this 

 role is. Various theories concerning the matter have been put 

 forward in recent years. For example, Overton, in 1901, pre- 

 sented the idea that every living cell is surrounded by a semi- 

 permeable membrane consisting of lipoid material, which regu- 

 lates the passage into and out of the cell of substances necessary 

 to its metabolism and growth. Recent investigations by Oster- 

 hout and others indicate, however, that Overton's hypothetical 

 lipoid membrane is not essential to a proper explanation of the 

 migration into and out of the cell protoplasm of nutritive materials, 

 etc. Other investigators have cited results which appear to indi- 

 cate that lipoids play an important, but as yet unknown, part in 

 the process of fat metabolism. Others go even further than this, 

 and argue that since the extraordinary rapidity of the chemical 

 changes which take place in plant protoplasm indicates the 

 necessity of the presence there of exceedingly labile substances, and 

 since both fats and proteins are relatively stable compounds, it is 

 possible that the lipoids, which contain both nitrogenous and fatty 

 acid groups, play an exceedingly important part in the metabolism 

 processes. Bang, in particular, has pointed out (in 1911) that the 

 lipoids are probably the most labile of all the components which 

 constitute the colloidal system known as plant protoplasm. The 

 importance of such considerations will be more apparent after the 



