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POPULAR SCIENCE REVIEW. 
Max Wichura,* in his paper on hybrid Willows, admirably 
shows the various degrees of sterility obtaining in the fruit of 
such hybrids. Thus, epitomizing his remarks : — 
1. Catkins wither quickly, like those unimpregnated. 
2. Ovaries swell and ripen, but have no seed. 
3. Ovaries are filled with silken hairs. 
4. Seeds are present, small and incapable of germination. 
5. Seeds apparently perfect, but do not germinate. 
6. Seeds germinate by young plants are weak, and soon 
perish. 
M. Naudin further observes, that sterility takes effect much 
more on the pollen than on the ovules. This, too, quite agrees 
with Wichura^s observations, who describes very minutely the 
various degrees of degeneration in the pollen, and the appear- 
ance that the grains present in hybrid willows, stating that 
“ a tolerably correct opinion may be drawn of the sterility of 
a willow by a mere examination of the pollen,” and that certain 
laws seem to prevail in the gradual sterility of the pollen. 
1. The anomaly of the pollen increases with the succession of generation 
arising from the fertilizing of hybrids with their own pollen. 
2. Different individuals of the same generation resemble each other in the 
imperfection of their pollen. 
3. Distantly related willows give a more irregular pollen. 
4. Anomaly of pollen increases with the number of intermingled species. 
Naudin furnishes us with the instance of Nicotiana glauca 
+ angustifolia. In this hybrid the pollen is totally defective, 
while the ovary grows by the impregnation of pollen from 
N. Tabacum and JSf. macrophyllum and he adds the following 
important generalization : — 
All the hybrids which I have examined having some grains of pollen 
good have been fertile, often to a high degree, by their ovaries. No example 
is known where a plant, being sterile by its ovary, is yet fertile by its anthers, 
even in the most feeble degree. That sterility should take effect first on the 
pollen is not surprising, as that is the most elaborated or 1 animalized ’ of all 
the plant organs. 
2. The inequality that obtains in the results of attempting to 
cross plants. — M. Naudin remarks that if some hybrids are 
sterile by their stamens and ovary, others, and perhaps a great 
number, are fertile. Of these last, some by their ovary alone, 
others by both pollen and ovary, but never so by pollen alone. 
Hybrids are fertile by themselves every time their anthers 
contain well-organized pollen. 
3. The aptitude of species to cross, and the fertility of hybrids 
* The Journal of the Horticultural Society , Yol. I. p. 57. 1866. (New 
Series.) 
