REPRODUCTION. 665 



extrusion of the polar body in the development of gametes, 

 we find that there is reason to regard it as of profound 

 physiological significance. There is, in the first place, the 

 fact that a gamete, in the development of which the ex- 

 trusion of a polar body has taken place in any form, is, as a 

 rule, incapable by itself of developing into a new individual. 

 In the second place, there are, in families of plants in which 

 the differentiation of the gametes is usually accompanied by 

 the extrusion of a polar body, instances in which this process 

 does not take place ; and in these instances the cells pro- 

 duced are not gametes, but parthenogenetic spores. 



Of these two points, the first is sufficiently clear not to 

 require elucidation, but it will be advantageous to illustrate 

 the second. The case which we will take is that of the 

 Saprolegnieae (see p. 619). Pringsheim observed, and his 

 observations have been confirmed by de Bary, that under 

 certain circumstances plants of Saprolegnia ferax and of 

 Achlya polyandra bear no antheridia, and yet their oogonia 

 produce oospores ; and, as we know, de Bary has come to the 

 conclusion that even when antheridia are present, no sexual 

 process takes place. The oospores of the Saprolegnieae are 

 then parthenogenetically produced, and this is probably to be 

 correlated with a peculiarity in their development. In the 

 allied Peronosporeae the development of the oosphere, as 

 already stated (p. 619), depends upon the differentiation of 

 the protoplasmic contents of the oogonium into ooplasm and 

 periplasm. This differentiation does not take place in the 

 oogonium of the Saprolegnieae ; still there is not an indication 

 of it. During the development of the reproductive cells, 

 the protoplasm of the oogonium is in active movement, and 

 portions of it are from time to time thrown off. These 

 portions doubtless correspond to the periplasm in the oogo- 

 nium of the Peronosporeae ; but in the Saprolegnieae the sepa- 

 ration of the periplasm is only temporary, for the extruded 

 portions subsequently coalesce with that from which the 

 reproductive cells are formed. The explanation of the fact 

 that the reproductive cells formed in the oogonia of the 

 Saprolegnieae are oospores and not oospheres, appears to be 



