76 MAINE STA.TE COLLEGE 



Any one can perform the mechanical operation of crossing plants, 

 but the haphazard uniting of individuals is of little value. To 

 breed plants intelligently we must have a distiact type in mind and 

 work toward our ideal. In order to do this we must have some 

 conception of the effects likely to be produced. The most promi- 

 nent effects of crossing, as would be expected, are seen in the 

 offspring ; and it is of the greatest importance that care be used in 

 the selection of parents. If the parents are very different in char- 

 acter the offspring will probably be weak. But the converse is also 

 true : A cross between closely related species or races is more 

 vigorous than its parent. It is well proved that "crossing is good 

 for the resulting offspring because the differences between the 

 parents carry over new combinations of characters or at least new 

 powers into the crosses. It is a process of revitalization."* 



The limits to which cross-breeding is either possible or profitable 

 are not yet well understood. As a rule closely related species will 

 cross readily while widely different species cross with difficulty ; but 

 this rule has very marked exceptions. It seems impossible to cross 

 any of the varieties of winter squash — Ciiciirhita maxima — such as 

 Hubbard, Sibley, etc., with varieties of summer squash or with the 

 pumpkin — Ciccurbita pepo ; — while we feel safe in saying the cucum- 

 ber and the muskmelon cannot be crossed. 



In selecting parents the question naturally arises as to which 

 shall be made the male and which the female parent in order to 

 produce certain probable results. It was formerly held that in case 

 of a hybrid the female parent gives constitution and vigor while the 

 male parent gives form, size, color, etc. But at the present time 

 it is generally conceded that the results will be approximately the 

 same no matter which is used as the male or the female parent. 



It is not always possible to select our male and female parents at 

 will. In other words, reciprocal crosses are not always possible. 

 For example, I may cross a yellow bush scalloped squash with the 

 summer crook-neck, but I have never yet been able to cross the 

 crook-neck with the bush scalloped. Other cases of a similar 

 nature are not infrequent. Why is this failure? Is it due to a 

 constitutional peculiarity ; to the form of the ovarium ; to a weak- 

 ness of the pollen of the one species or variety, or what may be 

 the underlying cause? The question is j^et one of the unsolved 

 problems. 



* Cf. Bailey, Cross Breediug and Hybridizing-, p. 13. 



