124 THE COTTON PLANT IN EGYPT chap. 



from Arizona, from the Sudan, etc. More than this, it has 

 contained plants of Fj, Fo. F3, F4, F5, and Fg, raised from 

 crosses between American Uplands and Egyptian. Con- 

 fining our discussion for the sake of simplicity to the Fj of 

 such crosses, it is olivious that we possess an infinite 

 variety of pollen grains on an acre of land. To estimate 

 the number of allelomorphic pairs involved in the cross of 

 " 38 " (King) with " 89 " (Charara) at fifty would be very 

 conservative. The number of possible combinations of 

 these pairs works out at a figure which, for our present 

 purpose, we may consider as infinite. Now, if Mendelism 

 is not a delusion, this infinite number of combinations 

 corresponds with an infinite variety of nuclear composi- 

 tion, on the part of the male gametes. It is true that 

 these gamete-nuclei are devoted to sexual purposes, but 

 their relations, the vegetative nuclei of the pollen grains, 

 are generally admitted to control the growth of the pollen- 

 tube, and these are of identical composition with the 

 gamete nuclei. Consequently, we may reasonably expect 

 to find some correlation, however indirect it may be, 

 between the gametic differences and the physiological 

 difi'erence.s in growth-rate of the pollen-tube. iSuch relation 

 would imply a greater " variability " in the growth 

 processes of pollen tubes from an Fi flower than that 

 which we find in a pure strain. The standard deviation, 

 or probable error, in the behaviour of Fi pollen-tubes 

 under a given set of conditions would necessarily be much 

 greater than that of the pollen-tubes in a pure strain, 

 whether Egyptian or American. 



Regarded in another way, this conclusion may be stated 

 thus. If 3 per cent, of the pollen-tubes from Upland 

 pollen fluctuate sufficiently in a positive direction to enable 

 them to beat 3 per cent, of the Egyptian pollen-tubes in a 

 race down an Egyptian style, then we may expect — 

 owing to greater variability — that much more than 3 per 

 cent, of Fi plant poUen-tubes will vary sufficiently in a 



