2c5 Ostenfeld. 



II. 



Hybridization Experiments. 



In my paper of 1906 I reported that I had artificially produced 

 the following hybrids: 



H. pilosella x aiirantiacinii 



H. excellens x aiirantiacuiu 



H. excellens x pilosella. 



My method of crossing was as simple as possible: I isolated 

 under bell-jars before unfolding some heads of the plants I wished to 

 use. When a few days later the heads had opened — at any rate 

 the outer flowers of the heads — I picked off the head whose pollen 

 was to be used and rubbed it cautiously to and fro over the stigmas 

 of the head of the plant to be used as mother parent; this manipula- 

 tion was sometimes repeated one or two days later with a new head 

 of the father plant, but with the same one of the mother plant in 

 which now the more central flowers of the head had opened. The 

 head thus pollinated was kept continually under the bell-jar, closed 

 below with wadding, until sometime after the flowers had withered. 

 As soon as the withered corollas, on touching, easily dropped off in 

 a clump, the wadding was removed, as it caused the air in the jar 

 to be continually saturated with vapour and thus sometimes furthered 

 an attack of mould on the heads. The head was now permitted to 

 ripen under the bell-jar, but with free access of the air from below. 

 The jar only served to prevent the ripe fruits from being carried 

 away by the wind, if the gathering happened to be a little delayed. — 

 In the sowing of the fruits, the same precautions were taken as have 

 been mentioned under the castration experiments. 



This method, which I still use, is thus much simpler than that 

 used by Mendel (1870) and F. Schultz (1856), and it has the 

 shortcoming that it does not give results which can be used for 

 counting, self-fertilization (when the mother plant is hermaphrodite) 

 not being excluded; but I consider it as the only easily practicable 

 method when working with Compositae that have small flowers. 



F. Schultz transferred, by means of a fine brush, the pollen on 

 to the stigmas, but did not take special precautions against self- 

 fertilization; his method is thus not more exact than mine, but more 

 difficult to carry out. 



On the other hand, Mendel's method is the most exact; by means 

 of fine pins he removed the anthers before the opening of the flower 



