VARIATION OF CHEOMOSOMES 149 



be the more common procedure. A few examples will 

 illustrate what has been found out so far concerning some 

 of these possibilities. 



The evening primrose, CEnothera lamarckicma, has 14 

 chromosomes as its full or somatic number, and 7 as its 

 reduced number (Fig. 58, a), and these numbers charac- 

 terize most of the mutant types that De Vries found. But 

 there is one mutant known as gigas, that has 28 chromo- 

 somes as its full number, and 14 as its reduced number 

 (Fig. 58, b). Stomps estimates that gigas appears about 

 9 times in a million cases, i.e., in 0.0009 per cent. Gigas is 

 distinguished from Lamarckiana in many details of struc- 

 ture, but chiefly in its thick stem, etc., which is associated 

 with larger cells. 





?i5f m 



IPS 



a o c 



Fig, 58. — Chromosome group of CEnothera lamarckiana, a; chromosome^of [group"of O. 



gigas, b; triploid group, c. 



The type breeds true, i.e. .it does not revert to Lamarck- 

 iana; thus De Vries grew a family of 450 individuals from 

 his original gigas, only one being a dwarf gigas, viz., 

 nanella. The way in which gigas originates has been 

 much discussed, but no conclusion reached. De Vries 

 suggested that it is produced by an egg with 14 chromo- 

 somes (diploid), being fertilized by a sperm with 14 

 chromosomes, both of these diploid cells originating by 

 the suppression of a cytoplasmic division in the develop- 

 ment of the gametes. It has also been suggested that a 

 tetraploid condition might arise in a spore mother cell 

 that developed without fertilization (by apospory) . Gates 

 pointed out that by suppression of the first division of the 

 egg, after fertilization, the tetraploid condition would 

 arise. The only objection to this last view, that seems 



