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bilities of error which are worth considering, are 1°, that the pollen- 

 grains might have germinated in the anthers before we castrated 

 the head, and 2°, that the stimulus of castration might have been 

 the exciting cause of the development of the embryo. Although 

 both those suppositions seem improbable, they cannot be refuted 

 until other experiments with an exclusively female species has 

 reduced the possibility to zero. 



The castrated flower-heads develop like the un-wounded ones, 



next spring and always in baked soil to prevent foreign seeds. 

 When they had germinated, most of them were thrown away, but 

 in some case the plants have been kept for other purposes. 



With regard to the determination of the species it has been a 

 very difficult business, and indeed it is practically impossible 

 for one who is not a specialist to identify the species in this 

 genus. I have done my best, but I fear that some names may be 

 wrong. For some of the species Mr. Dahlstedt of Stockholm 

 has kindly given me the names, and I wish here to express my 

 best tanks to him for his valuable kindness. In our case a deter- 

 mination going to the elementary species is also not necessary; 

 when the collective species is correct, it will be sufficient. 



but are easily recognizable by their 

 shortness (see the text-figure) ; when 

 the fruits are fully ripened, they 

 force the bracts backwards as usual, 

 but the aspect of such an opened 

 castrated head with fullgrown fruits 

 is rather curious because of the 

 short pappus-rays. 



The plants used in the experi- 

 ments have all grown in the open 

 ground except some few which 

 were transplanted into pots and 

 isolated in a cold-house, but no 

 other precautions were taken, and 

 the castrated heads developed, un- 

 covered, from the time of castra- 

 tion to the harvest of the fruits. 



Fig. 1. Three heads of Hieracium 

 sp., of which two grow out after 

 castration. 



The fruits were sown as soon 

 as possible, partly in the autumn 

 of the same year, and partly in the 



