WHITE— STUDIES OF INHERITANCE IN PISUM. 547 



dwarfs are composed of many pure lines differing in a minor degree 

 as to height, number of internodes, etc. 



7. Fasciation, Umbellate Inflorescence. 



Most varieties of peas have either robust or slender, angular 

 or roundish stems, which are small at their base and three or four 

 times the basal diameter at their top or flowering region. The 

 flowers of such varieties are in ones, twos or threes on axillary 

 peduncles along a large stretch of the stem. These are the common 

 or " normal " characteristics of peas. 



Fasciation in peas greatly alters the above characters by in- 

 creasing the maximum width of the stem at the top from i cm. to 

 as much as 4 cm. The stem in this region either presents the ap- 

 pearance of a flattened, pressed cylinder or of an irregular cylinder, 

 with side splits and an opening in the top. Leaves as well as 

 branches grow out from this inside tissue region. The leaf arrange- 

 ment or phyllotaxy ceases to be regular in the fasciated region of 

 such plants, and the flowers instead of being axillary are bunched 

 together at the top of the stem in what may be called an irregular 

 umbel or bouquet. Not uncommonly in these fasciated plants, growth 

 is so uneven on opposite sides of the stem as to cause a curling up of 

 the stem making it resemble one side of an Ionic capital or a ram's 

 horn. Both Lobel and Gerarde mention and picture a fasciated 

 variety of pea in their herbals, and according to all observers the 

 character is strictly hereditary. In my own experience, seed of a 

 fasciated variety obtained from Eckford of Wem, England, has 

 always bred true to fasciation under every and all sorts of con- 

 ditions. Fasciation does appear in other plants and in peas, how- 

 ever, which is not inherited, but is mainly due to environmental 

 conditions. Further this type (8.5) is morphologically indistin- 

 guishable from the inherited type. Blodgett (8.5) cites a case in 

 which 90 per cent, of the peas of fields grown for canning pur- 

 poses were afflicted with this trouble, making the crops worthless 

 except for green manure purposes, since fasciated peas bear but 

 few pods and only when conditions are just exactly right. I have 

 seen this same type of fasciation in greenhouse cultures a couple 

 of times. 



PROC. AMER, PHIL. SOC, VOL. LVI, JJ, DECEMBER II, I917. 



