BIOTYPES AND HYBRIDS. 9 



elongated than is normal, and the lobing more shallow and therefore less 

 characteristic, so that it was less easy to estimate the uniformity and dis- 

 tinctness of the several pedigrees than when they were grown under more 

 favorable conditions. Even specimens belonging to the most deeply and 

 distinctly lobed families, when grown in the darker portions of the room, 

 retained their unlobed, juvenile type of leaf throughout life, sending up a 

 weak flower-stem from the juvenile rosette, and in such cases the relation- 

 ships could not be recognized, since the early leaves of all the forms studied 

 are very similar. The same difficulty was also experienced in the propa- 

 gating-house when the members of certain families were allowed to remain 

 too long crowded in the seed-pans. The offspring of these juvenile plants 

 have not been extensively studied , but from several families evidence has 

 accumulated which indicates that when again given favorable conditions 

 the offspring of these characterless plants return to the characters of the 

 family from which they sprang. 



In all cases the seeds have been sown in soil sterilized in an autoclave 

 in the manner usually adopted by students of pedigree-cultures, and the 

 efficiency of the method is inferable from the fact that in all these cultures 

 only 3 seedlings occurred whose origin was unknown. These unexpected 

 seedlings were an Oxalis, a Mo Hugo, and an Erechtites, and it does not seem 

 likely that any of these withstood the long-continued high temperature of 

 the autoclave, but rather that they were blown through the ventilators of 

 the propagating-house in a heavy wind-storm. 



It was soon demonstrated that Bursa has many features which make it 

 advantageous material from a technical point of view for pedigree-culture 

 work. The habit of the plant, consisting as it does of a moderately lax 

 rosette and nearly naked, erect flower- stem, allows the preservation of the 

 rosettes as herbarium specimens whose characters are almost as easily 

 studied as are those of the living plants, and the inflorescence may be cov- 

 ered with paraffin-paper bags to prevent chance crosses with other speci- 

 mens without appreciably interfering with the photosynthetic work upon 

 which the healthy development of the plant depends. 



The small size of the plants makes it possible to raise them to maturity 

 in 3-inch pots in many of the forms, though it is usually found advanta- 

 geous to repot to 4-inch pots those which it is desired to keep for seed. 

 This quality allows a large number of specimens to be raised in a small 

 compass. 



In most instances the life-cycle is short, requiring only 3 to 4 months 

 between the sowing of the seed and the gathering of the ripe seed of the 

 earliest matured individuals. In several of the forms of B. bursa-pastoris , 

 and in B. heegeri, however, 8 to 9 months were needed. The seeds ger- 

 minate in 5 to 8 days without a period of rest, thus making it possible to 

 accumulate data from a number of successive generations in a short time. 



