308 THE CELL 



Hence Maupas is of opinion that cross fertilisation between 

 individuals of different origin is necessary for Infusoria also. 



The ineffectuality of self-fertilisation has also been proved in 

 certain cases amongst Phanerogamia. Hildebrandt (VII. 24, p. 

 66) says of Gory dolls cava : "If a flower of this plant, in which 

 the opened anthers lie close to the stigma, be protected from 

 fertilisation by insects, no fruit is ever formed in it ; that this 

 is not due to the circumstances of the pollen not coming in con- 

 tact with the susceptible part of the stigma may be seen from the 

 fact that even those flowers, whose stigmata were powdered with 

 the pollen of the surrounding anthers, were non-fertile." 



" A perfect fruit can only develop when the pollen of the flowers 

 of one plant is placed on the stigma of another ; it is true that 

 fruit is formed when the flowers of the same vine are crossed - t 

 but the resulting plants produce a much smaller number of 

 seeds than is normal, and further they do not always come- 

 to perfect maturity." 



A similar absence of result after self- fertilisation has been 

 observed in a few other plants, i.e. certain species of Orchids, 

 Malvaceae, Reseda, Lobelia and Verbascum. 



Unfortunately, no very thorough investigation concerning the 

 behaviour of hermaphrodite animals has been made ; the diffi- 

 culties of such research would be very great. No doubt cases 

 would be also found here in which no fertilisation occurs between 

 the eggs and spermatozoa of the same individual when they are 

 artificially brought into contact ; with snails, for instance, this 

 must be the case. 



However, in opposition to the above-mentioned examples,, 

 we find others, which prove both that complete sexual affinity 

 does exist, and also that normal development by self-fertilisation 

 does take place between sexual cells, which are very nearly re- 

 lated to one another. 



Thus in the case of certain Conjugate (Rhynchoncvia) sister- 

 cells unite with one another, or, as in Svirogyra, cells which 

 belong to the same filament conjugate together {vide p. 283). 



Further, in many Phanerogams not only can the egg-cells be 

 fertilised with the pollen of the same flower, but the resulting 

 plants are strong and healthy ; and, moreover, this in-breeding 

 can be continued through many generations with equally happy 

 results. 



Between the two extremes the absence of any sexual affinity 



