Systematic Atavism 641 



veloping to unusual size, is afforded by a variety 

 of corn, which is called Zea Mays cryptosperma, 

 or Zea Mays tunicata. In ordinary corn the 

 kernels are surrounded by small and thin, incon- 

 spicuous and membranaceous scales. Invisible 

 on the integrate spikes, when ripe, they are 

 easily detected by pulling the kernels out. In 

 cryptosperma they are so strongly developed as 

 to completely hide the kernels. Obviously they 

 constitute a case of atavism to the characters 

 of some unknown ancestor, since the corn is the 

 only member of the grass-family with naked 

 kernels. The var. tunicata, for this same rea- 

 son, has been considered to be the original wild 

 form, from which the other varieties of corn 

 have originated. But as no historical evidence 

 on this point is at hand, we must leave it as it is, 

 notwithstanding the high degree of attractive- 

 ness attached to the suggestion. 



The horsetail-family may be taken as a fur- 

 ther support of our assertion. Some species 

 have stems of two kinds, the fertile being 

 brownish and appearing in early spring before 

 the green or sterile ones. In others the stems 

 are all alike, green and crowned with a cone- 

 like spike of sporangia-bearing scales. Mani- 

 festly the dimorphous cases are to be considered 

 as the younger ones, partly because they are 

 obvious exceptions to the common rule, and 



