Retrograde Varieties 139 



pubescence in some hairy species, as in Galeop- 

 sis Ladanuni canescens, Lotus corniculatus 

 hirsutus and so on. But Veronica scutellata is 

 smooth and has a pubescent-variety, and Cyti- 

 sus prostratus and C. spinescens are each re- 

 corded to have a ciliate form. 



Comparable with the occurrence and the lack 

 of hairs, is the existence or deficiency of the 

 glaucous effect in leaves, as is well known in the 

 common Ricinus. Here the glaucous appear- 

 ance is due to wax distributed in fine particles 

 over the surface of the leaves, and in the green 

 variety this wax is lacking. Other instances 

 could be given as in the green varieties of Pap- 

 aver alpinum and Rumex scutatus. No positive 

 instances are recorded in this case. 



Spines and prickles may often disappear and 

 give rise to unarmed and defenceless types. 

 Of the thorn-apples both species, the white- 

 flowered Datura Stramonium and tlie purple 

 D. Tatula have such varieties. The spiny 

 form has a variety called the '' Dutch," 

 which lacks the prickles of the fruit ; it is a very 

 old form and absolutely constant, as are also 

 the thornless thorn-apples. Last year a very 

 curious instance of a partial loss of prickles was 

 discovered by Mr. Cockerell of East Las Vegas 

 in New Mexico. It is a variety of the American 

 cocklebur, often called sea-burdock, or the 



