OTHER MENDELIAN CHARACTERS 29 



pod. It is not, however, until this stage in the 

 development of the pod is reached that the difference 

 between the yellow and the green pod can be observed. 

 And, lastly, the colour of the seed-coat cannot be 

 seen, because it is not developed, until the pod, con- 

 taining it, is ripe and dry. 



It will be noted that in the above recapitulation 

 the five characters have been placed in the order in 

 which we have considered them in detail, and also 

 in the order in which they appear on the plant. 



There remain two characters of the pea dealt with 

 by Mendel ; but they will be taken out of their order. 

 They are the earliest of all to appear ; so early, 

 indeed, that they can be seen before the seed is 

 planted — i.e. as soon as it is taken out of the pod. 

 It will be remembered that the earliest character 

 which we have yet considered (the distinction 

 between tallness and dwarfness) was visible in the 

 young seedlings. The two characters still to be dealt 

 with belong to the first two leaves of the plant which 

 remain in the seed, and never come above the ground. 

 These first two leaves, or cotyledons, are so important 

 economically, because they contain the food-material 

 (starch and sugar) which renders the pea valuable 

 as food, and the characters in respect of which they 

 differ have played so prominent a part in estab- 

 lishing the reality of the Mendelian phenomenon, and 

 in testing the theories put forward to explain it, that 

 a special chapter will be devoted to their consideration. 



Let us now take a general survey of the five 



