184 STEMS 



dissimilarities as to a number of characters. By using a 

 number of characters rather than just one, botanists have 

 been able to determine what are the natural great groups 

 of plants ; that is, those groups which have resulted 

 from the processes of nature. Similarly, the processes 

 of nature, working through long ages, have formed the 

 natural groups of mankind, and we do not distinguish 

 a white man from an Indian by one character, but by a 

 number of characters. 



It took botanists a long time to find out the real kin- 

 ships of the great groups of plants, and even now the 

 system of plant classification is revised from time to time 

 in the light of newly discovered facts. Thus, for example, 

 a plant which was thought for a long time to be a sort of 

 cousin of another kind of plant may be found to have 

 certain characters which prove it to be no such relation 

 at all, but the kin of quite another family of plants. 



You know already that there are two great types of stem 

 structure among seed plants. Not many years ago bota- 

 nists divided all seed plants on the basis of these two types 

 of stem structure. Plants with scattered vascular bundles 

 were called endogens; those with the cylindrical arrange- 

 ment were called exogens. It was found, however, that 

 this was not a natural division and the system had to be 

 readjusted. Yet stem structure is still used as one of the 

 great characters upon which classification is based. You 

 should know which of the great groups have the cylindrical 

 arrangement and which have the scattered arrangement. 



It is the monocotyledons which have the scattered 

 arrangement. All the members of the grass family are 

 monocotyledons. This great family includes all the 

 cereals. Bamboo is the largest member of this family. 



