8 Colour and other Characters in the Potato 



below the base of the flower there occurs a ring of cork. In all 

 potatoes the flowers have a great tendency to separate at this point 

 from their stems : the tendency is more marked in those flowers 

 where the anthers are sterile. If such a flower is used as the female 

 parent the chances of a successful cross fertilization are somewhat less 

 good than if the fertilization is made on one with fertile anthers owing 

 to this habit of separation. In all potato plants, however, when grown 

 out in the open, successful fertilization, be it " selfing" or "crossing," is 

 a hazardous undertaking, and I personally do not succeed in getting 

 more than about "5 % of the individual flowers I handle to set seed. 



Once the ovary begins to swell there is little fear of separation 

 taking place at the cork ring, indeed the stem gradually thickens and 

 carries the berry late into the autumn. 



All my work has been carried on without placing the flowers in 

 bags. The reasons for not adopting special precautions were that 

 when bagged the flower invariably drops, that bees and the like never 

 approach a potato flower though a small fly often lives in the bottom 

 of the corolla, that the flower is constructed for self-fertilization, and 

 that the quantity of pollen is so scanty as to render fertilization by the 

 wind in the highest degree improbable. Each year I have sterilized a 

 number of flowers and purposely left them unpollinated, in no instance 

 has any fertilization taken place. In two instances out of some 

 hundreds so treated the ovaries swelled till they attained a diameter 

 of 3/16 in., but they contained no seed and dropped. 



Although the potato, owing to its scanty pollen, its frequent 

 sterility, and its delicate flower, is not an ideal subject for Mendelian 

 research, it does still off"er to the experimentalist one redeeming char- 

 acter. An individual plant can always be "carried on " by means of its 

 tubers into the next season's work, and whether it be for the sake of 

 comparison or for the purposes of further fertilization this property is 

 of the utmost service. 



The Scope of the Observations. Attention has been concentrated 

 mainly on the heredity of characters of the tubers, for the haulm or 

 foliage of the potato plant, though variable in habit of growth, size, 

 shape, texture and colour, does not lend itself readily to this type of 

 work. The foliage more especially is so variable in different parts of 

 the same plant, whilst the differences between one type of foliage and 

 another, however apparent, are so difiicult to define that except in one 

 instance, which will be considered later in detail, I have not made out 

 anything sufficiently definite. 



