110 



HOW CROPS GROW. 



much simpler red crystalline substance, Haemaeetin, yield- 

 ing about 96 per cent of the former and 4 per cent of 

 the latter. Haematin has approximately the formula 

 CsaH^N^FeOs, so that the proteid, though simpler than 

 haemoglobin, must have an extremely complicated mole- 

 cule, and it is, accordingly, difficult to decide whether a 

 few thousandths of the acids, bases or salts which may 

 be associated with these bodies, as they exist in plants or 

 pass through the hands of the chemist, are accidental or 

 essential to their constitution. 



Occurrence in Plants. Aleurone. It is only in the 

 old and virtually dead parts of a living plant that albu- 

 minoids are ever wanting. In the young and growing 

 organs they are abundant, and exist dissolved in the sap 

 or juices. They are especially abundant in seeds, and 

 here they are often deposited in an organized form, chiefly 



$? 



Fig. 18. Fit,'. 19- 



in grains similar to those of starch, and mostly insoluble 

 in water. 



These grains of albuminoid matter are not, in many 

 cases at least, pure albuminoids. Hartiir, who first de- 

 scribed them minutely, has distinguished them by the 

 name aleurone, a term which we may conveniently em- 

 ploy. By the word aleurone is not meant simply an 



