The variability, however, in the successive generations of mongrels is, perhaps, greater than in hybrids. 查尔斯·达尔文.物种起源.
Many exotic plants have pollen utterly worthless, in the same condition as in the most sterile hybrids. 查尔斯·达尔文.物种起源.
We see this tendency to become striped most strongly displayed in hybrids from between several of the most distinct species. 查尔斯·达尔文.物种起源.
The above view of the sterility of hybrids being caused by two constitutions being compounded into one has been strongly maintained by Max Wichura. 查尔斯·达尔文.物种起源.
In regard to the sterility of hybrids, in which the sexual elements are imperfectly developed, the case is somewhat different. 查尔斯·达尔文.物种起源.
Altogether there is the closest identity in character and behaviour between illegitimate plants and hybrids. 查尔斯·达尔文.物种起源.
This greater variability in mongrels than in hybrids does not seem at all surprising. 查尔斯·达尔文.物种起源.
So it is with hybrids, for their offspring in successive generations are eminently liable to vary, as every experimentalist has observed. 查尔斯·达尔文.物种起源.
The fertility, both of first crosses and of hybrids, is more easily affected by unfavourable conditions, than is that of pure species. 查尔斯·达尔文.物种起源.
We will now look a little closer at the probable nature of the differences between species which induce sterility in first crosses and in hybrids. 查尔斯·达尔文.物种起源.
It is not always equal in degree in a first cross and in the hybrids produced from this cross. 查尔斯·达尔文.物种起源.
From this extreme degree of sterility we have self-fertilised hybrids producing a greater and greater number of seeds up to perfect fertility. 查尔斯·达尔文.物种起源.
Quatrefages states that the hybrids from two moths (Bombyx cynthia and arrindia) were proved in Paris to be fertile inter se for eight generations. 查尔斯·达尔文.物种起源.
Why, it may even be asked, has the production of hybrids been permitted? 查尔斯·达尔文.物种起源.
With hybrids raised from the same seed-capsule the degree of sterility is innately variable, so it is in a marked manner with illegitimate plants. 查尔斯·达尔文.物种起源.
We will now consider a little more in detail the laws governing the sterility of first crosses and of hybrids. 查尔斯·达尔文.物种起源.
The hybrids, moreover, produced from reciprocal crosses often differ in fertility. 查尔斯·达尔文.物种起源.
Between the sterility thus superinduced and that of hybrids, there are many points of similarity. 查尔斯·达尔文.物种起源.
Now the fertility of first crosses, and of the hybrids produced from them, is largely governed by their systematic affinity. 查尔斯·达尔文.物种起源.
And in this case, it is not at all surprising that the inherent sterility in the hybrids should have gone on increasing. 查尔斯·达尔文.物种起源.
First crosses between forms, sufficiently distinct to be ranked as species, and their hybrids, are very generally, but not universally, sterile. 查尔斯·达尔文.物种起源.
Both hybrids and mongrels can be reduced to either pure parent form, by repeated crosses in successive generations with either parent. 查尔斯·达尔文.物种起源.
Now, hardly any cases have been ascertained with certainty of hybrids from two quite distinct species of animals being perfectly fertile. 查尔斯·达尔文.物种起源.
He who will explain these latter cases will be able to explain the sterility of hybrids. 查尔斯·达尔文.物种起源.