disco:n'ti]S[uous variation. 65 



course premature." The steps in seed evohitiou arc l>rieflj 

 summarized in the following paragraph : 



^'The history of the seed, as I read it from the imperfect 

 and fragmentary data that are available, has been a series of 

 advances spread over long geological periods. The possibilities 

 of the seed-habit were realized onlv l>it bv bit, and the high 

 efficiency of the modern seed depends in large degree upon 

 the close association of other structures which co-operate in its 

 functions. jSTo doubt the first step, the retention of the mega- 

 spore, was the most important of all ; though, that this might 

 be effective, some contrivance for the capture of the pollen- 

 gTains must have accompanied it. Later steps in the process 

 of seed-evolution would include the adjustment of an intrasem- 

 inal embryonic stage, and in time the substitution of the pollen- 

 tube for the liberation of sperms." 



The great difficulty of conceiving how such a result could 

 be achieved by the process of continuous evolution, and the 

 lack of sufficient data to give such a theory a firm foundation in 

 fact, are clearly recognized, and the speaker continues as 

 follows : 



"^'JSTow, assuming, as I think we are entitled to assume, that 

 seeds have come into existence along some such lines as those 

 thus crudely blocked out, there is a great difficulty in conceiving 

 the process other than discontinuous. Every one of the stages 

 emphasized involves the conception of something more abrupt 

 than mere gradual variation. And tliere is, of course, the old 

 difficulty confronting us as to how the organ or mechanism came 

 to be preserved at its inception. All these difficulties vanish 

 when it is recognized that effective variation is of the discontinu- 

 ous order, and that the suceessive chanees involved mav be con- 

 siderable enough to be desigiiated jumps. Happily such views, 

 based upon experimental results, have been formulated by De 

 Yries in his Mutation Theory. That theory is so well known to 

 botanist>s in this country that any exposition here is quite 

 superfluous. The least thing that can be said in its support is 

 that it is perfectly tenable. But we may go much further 



