34 



DE. E. E. GATES— CONTEIBUTION TO A 



evident tliat tlie Oenotheras cultivated in Botanical Gardens have for years heen exliibiting 

 phenomena of mutation closely similar to or identical with, those studied by DeVries in 

 his garden. Certain of these new forms, sucli as O- cognata, have been noticed by 

 irdeners, given names, and made the basis of new local races. Their origin is just 

 as sudden and discontinuous in Botanical Gardens as in experimental plots, and is 

 therefore clearly not due to continued selection. Each race appears, at once, full-fledged, 

 the descendant of a single aberrant individual. 



6 



O. nanella. 



I have grown hundreds of plants of O. nanella, and while they exhibited a wide 

 range of leaf-form, yet they have never been found to give rise to mutants. 0. nanella 

 has never been known to throw any of the other mutants, and, in this respect, it differs 

 from several of the other types. But in very large cultures, dwarfs having tlie 

 characters of other mutants sometimes appear from O. nanella. Thus (Zeijlstra, 1911) 

 18,649 plants of O, nanella derived from a previous generation were without exception 

 dwarfs, but three of them possessed oblonga and one elliptica characters. O. nanella 

 itself diflers from O. Lamarchiana not only in stature but in leaf and flower 

 characters. 



The rosettes of O. nanella in my cultures are more variable than those of any other 

 mutant except O. gigas. These variations will not be illustrated here, but the buds are 

 shown, two-thirds natural size, in PL 3. fig. 41, with a bract attached to one. The 

 bud-cone is usually shorter and slenderer than in the other forms. 



Dwarf or nanella forms of nearly all the mutants are now known, including 0. lata 

 nanella, 0. gigo,s nanella, 0. nanella-ohlonga, O. nanella-alhida, O. nanella-elUptica, and 

 O. nanella-scintillans. 



Begarding the nature and cause of the dwarf character of O. nanella, Schouten 

 (1908) has suggested that it results from a pathological condition of the plant, due to 

 bacterial action, and invokes Eriksson's mycoplasma theory to explain its hereditary 

 transmission. He states that the rosettes of O. nanella become sickly and die back ; but 

 careful observation has revealed nothing of this nature in my cultures, which shovA s 

 that the phenomenon he describes is due to some local condition. Zeijlstra (1911) lias 

 since found that a Micrococcus inhabits the cells of the stem in O. nanella in his 

 cultures, which indicates its greater susceptibility than other forms. That different 

 forms differ widely in their susceptibilities to fungal attacks, I have found to be true of 

 other species of Oenothera. Zeijlstra believes that the peculiar leaf-characters and the 

 very short internodes of O. nanella are a result of the parasite, because occasional side 

 branches appear which are dwarf yet have O. Lamarchiana leaf-characters and loi 

 internodes than the main stem. He therefore thinks that a dwarf O. Lamarckiana 

 appears as the result of a mutation, but that the parasite which attacks the dwarfs 

 distorts tliem and causes their development into the '* O. nanella " form. Whether a 

 |)arasite really produces this effect can only be determined by infection experiments. 

 Even if the hypothesis were true, it would remain unexplained why all the nanellas 

 which appear are affected. I have obtained several dwarf races, having quite unlike 



o 



