640 PHYSIOLOGY. 



morphological relations in the transformation and perfection of flowering 

 plants. 



The inferences drawn by Darwin, Hildebrand, Delpino, and others, 

 however, have lately been questioned by Henslow, whose conclusions are 

 as follows : 1. The majority of flowering plants are self -fertile. 2. Very 

 few are known to be physiologically self-sterile. 3. Many are morpholo- 

 gically self-sterile.- 4. Self-sterile plants become self-fertile (a) by 

 withering of the corolla ; (6) by its excision ; (c) loss of colour ; (d) 

 closing ; (e) not opening ; (/) absence of insects ; (a) reduction of tem- 

 perature ; (h) transportation. 5. Highly self -fertile forms may arise 

 under cultivation. 6. Special adaptations occur for self-fertilization. 

 7. Inconspicuous flowers are highly self -fertile. 8. Cleistogamous flowers 

 are always self-fertilized. 9. Conservation of energy in reduction of 

 pollen. 10. Relative fertility may equal or surpass that of crossed plants. 

 11. It does not decrease in successive generations. 12. It may increase. 

 13. Free from competition, self-fertilized plants equal the intercrossed 

 (a) as seedlings, (&) planted in the open ground. 14. They may gain no 

 benefit from a cross from the same or a different stock. 15. They are as 

 healthy as the intercrossed. 16. They may be much more productive 

 than flowers dependent on insects. 17. Naturalized abroad they gain 

 great vigour, and, 18, are the fittest to survive in the struggle for life. 



As regards the question of self-fertilization, or cross-fertilization, and 

 their respective consequences favourable or otherwise, it would seem that 

 both the views above cited, different as they seem, may be correct. What 

 is now required is a series of experiments and observations to ascertain 

 under what precise circumstances each method of fertilization is adopted 

 and the reasons and consequences thereof. 



Hybridization. 



Cross-breeding. The treatment of the subject of the sexual reproduc- 

 tion of Plants would be incomplete without some notice of the pheno- 

 menon of hybridization^ or cross-breeding between distinct species of 

 plants. 



From the difficulties arising partly from the minute size of the struc- 

 tures, partly from the comparatively recent date of any accurate know- 

 ledge of the sexual organs of Cryptogams, we are at present only 

 acquainted with a few certain facts in reference to the cross-breeding of 

 species in that Subkingdom. It has long been known, however, that in 

 collections of cultivated Ferns forms spring up from time to time pre- 

 senting new characters, more or less intermediate between well-known 

 natural species ; and these have been commonly accounted hybrids. The 

 discovery of the phenomenon of fertilization on the prothallia of Ferns 

 gives a new support to the supposition that such plants are hybrids, 

 although the question is still insufficiently supported by evidence. 



Cross-breeding in Algae. We possess, however, some facts of import- 

 ance on this subject relating to the Fucaceous Algae. Thuret took 

 advantage of the extrusion of the germ-cells and sperruatozoids in 

 Fucaceae before impregnation to collect these separately and experi- 

 ment on the degree to which hybridization was possible. He found that 

 spermatozoids of Fucus ferrate* and F. vesiculosus would not fertilize the 



