378 INTRODUCTION TO EMBRYOLOGY OF ANGIOSPERMS 



that the net result is the same and fertilization still fails to take 

 place. 



However, the main difficulty is not so much in the initial germi- 

 nation of the pollen as in the subsequent growth of the pollen tube 

 in a foreign style. This may be clue either to the fact that the 

 maximum length attainable by the pollen tubes of the male parent 

 is inadequate for enabling them to reach the ovules, or that the un- 

 favorable medium through which they have to make their way 

 causes an excessive retardation of their growth. 



When the failure of a cross is due to such causes, one obvious 

 remedy is to try the reciprocal cross, but frequently even this is 

 unsuccessful. An alternative method is to amputate the style and 

 reduce it to a suitable length. In a cross between Zea and Trip- 

 sacum, Manglesdorf and Reeves (1931) shortened the style of the 

 former to a length suitable for the pollen tubes of Tripsacum and 

 thereby obtained intergeneric hybrids. However, since the cut end 

 of the style is not always as suitable for pollen germination as the 

 stigma, sometimes it is desirable to use a different method in which 

 the middle portion of the style is removed and the upper and lower 

 portions are then joined together and held in place (Buchholz, Doak, 

 and Blakeslee, 1932). 



The Buchholz method, based on experiments with flowers of 

 Datura, may be briefly described as follows. On the plant which is 

 to serve as the maternal parent, a nearly mature unopened bud is 

 selected. One operator now makes a transverse cut through the 

 bud at the point k (Fig. 203 A, B), where the fluted inner surface of 

 the corolla shows a marked constriction. A second operator places 

 the style on a previously prepared gauge and makes a clean square 

 cut at the desired distance from the stigma, discarding the lower 

 part of the style. The newly cut end of the stigma-bearing portion 

 of the style is now inserted in a closely fitting grass straw, which is 

 lowered over the stump of the basal part of the style. The moment 

 the two cut surfaces come in contact, further lowering of the straw 

 gives an upward thrust to the part bearing the stigma. This en- 

 ables the operator to know when contact is made and the process is 

 complete. If the operation (Fig. 203A-H) is carried out carefully, 

 the pollen tubes pass down the joint and are able to reach the ovules. 

 A Japanese worker, Yasuda (1931), has gone one step further 

 and attempted an actual graft of the style upon the ovary in Petunia 



