GU ELEMENTS OF STRUCTURAL BOTANY. 



ters common to all of them, just as the group ending 

 with Willow was found to be marked by characters 

 possessed by all its members. The flowers of Dicoty- 

 ledons were found to have their parts, as a rule, in 

 fours or fives ; those of our second group have them in 

 threes or sixes, never in fives. 



78. Again, the leaves of these plants are straight- 

 veined, except in Trillium and Indian-Turnip, which 

 must be regarded as exceptional, and they do not as a 

 rule exhibit the division into petiole and blade which 

 was found to characterize the Exogens. 



79. We shall now compare the structure of a grain 

 of Indian Corn with that of the Cucumber or Pumpkin 

 seed which we have already examined (page 45). It 

 will facilitate our task if we select a grain from an ear 

 which has been boiled. And first of all, let us observe 

 that the grain consists of something more than the 

 seed. The grain is very much like the achene of the 

 Buttercup, but differs in this respect, that the outer 

 covering of the former is completely united with the 

 seed-coat underneath it, whilst in the latter the true 

 seed easily separates from its covering. Remove the 

 coats of the grain, and what is left is a whitish starchy- 

 looking substance, having a yellowish body inserted in 

 a hollow (Fig. 90) in the middle of one side. This latter 

 body is the emhrya, and may be easily removed. All 

 the rest is alhumen. Fig. 91 is a front view of the 



/■ — ^x embryo, and Fig. 92 shows a vertical 



V\ ] IM K section of the same. The greater part 



m\ ,/ tjl I Sy of the embryo consists of a singte cotyk- 



\' ^^ ^y don. The radicle is seen near the base. 



Kg. 90, Fig. 91 Fif.M. and the plumule above. 



80. Comparing the result of our observations with 



