142 Cross-Fertilisation in Potatoes. [may, 



is growing. The paper bag should then be removed, and the 

 copper wire straightened out ready to be reapphed. Before 

 proceeding with the operation of fertiUsation the operator 

 should sterilise his forceps and the thumb and forefinger of 

 his left hand by means of the alcohol in the bottle — the fingers 

 should be sterilised by allowing a few drops to run over them. 

 \^'Tien the alcohol has dried off, which it rapidly does in the 

 open air, he should seize one of the anthers at its basal attach- 

 ment with the forceps and hold it between the thumb and fore- 

 finger of the left hand in such a way that the line of dehiscence 

 of the right-hand lobe is uppermost. With the forceps in the 

 right hand the anther is gently split open ralong the line of 

 dehiscence with the point of one blade of the forceps, and in 

 so doing it will be found that a minute heap of white dust 

 accumulates on the point of the forceps. This is the pollen. 



The operator now very gentl}^ spreads the pollen on to 

 the stigma of the female flower. This should be done so 

 that the metal of the forceps scarcely touches the stigma 

 at all, and the pollen should be distributed over the whole 

 surface of the stigma. When the right-hand lobe of the anther 

 has been thus emptied it is quite easy to turn the anther over 

 in the fingers and expose the left-hand lobe and open that one 

 in a similar manner. Where the pollen is abundant two 

 flowers can be fertilised from each lobe, but this naturally 

 varies with the amount of pollen and the skill of the operator. 

 Having fertilised the flowers, the next step is to write the date 

 of the operation and the name of the paternal plant on the 

 label. The bag should then be replaced in exactly the same 

 manner as it was put on. Forty-eight hours after fertilisation 

 the operator should remove the bag and very gently nip off 

 the stigma, leaving the pistil standing. This done, it is 

 unnecessary to replace the bag. Within three or four days 

 the flower will droop and the corolla fall off, and if fertilisation 

 has been successful the individual flower stalk will thicken 

 and the little cork joint which is to be found normally about 

 I in. beneath each flower will become absorbed. At the 

 same time the ovary swells into a berry which in ordinary 

 varieties is round and like a tomato. 



Growth of th« Berry.— In most varieties the berry will grow 

 till it is about i in. in diameter, but it is highly advisable when 

 it has attained a size of about J in. in diameter to fix a bag 

 round it. The reason for this is that the berries must be left 

 until the haulm dies down, and when this occurs it frequently 

 happens that the berries either drop or are lost sight of at 



