K.— BOTANY. 237 



Historically this generalisation of Strasburger fell like a bomb-shell 

 into the midst of the old controversy between the rival theories of alterna- 

 tion, styled in the words of Celakovsky ' homologous ' and ' antithetic' 

 But it must be remembered that at the moment there was no complete 

 demonstration of a cytological alternation in any one Alga, though the 

 facts soon followed for Fuciis [Strasburger (1897), and Farmer and 

 Williams (1898)] ; and for Dictyota (Lloyd- Williams, 1897-8). We need 

 not recite again the arguments fro and con of that old discussion. It 

 soon lost its intensity in face of the obvious deficiency of crucial facts, 

 which alone could lead to some final conclusion. Loose comparisons 

 between organisms not closely allied are but the long-range artillery of 

 morphology. Comparisons between organisms closely related are its 

 small-arms. The discussions of the 'nineties of last century on alternation 

 were all engagements at long range, which could not be decisive without the 

 use of close comparison. As the necessary facts were not then in our hands, 

 those premature engagements might be held as drawn ; and it was open 

 to both parties still to entertain their own opinions. Meanwhile it may 

 interest us as spectators to note the relation that exists between homoplasy 

 as defined by Lankester in 1870, and those intimate questions that arise 

 from Strasburger's paper to this Section in 1894. The cytological facts 

 acquired since the latter date tend to confirm the normal constancy of a 

 nuclear cycle. Their effect has been to accentuate more than before 

 the inconstancy of the somatic developments related to it. Like the 

 fabulous genie let loose from its bottle, the conception of a nuclear cycle 

 in plants that show sexuality, disclosed in 1894 by Strasburger, dominates 

 ever more and more the morphological field. 



Before discussing the relation of somatic development to that cycle, 

 it will be well to revise the terminology. The word ' homologous ' has a 

 double significance, as shown by Lankester. If it be used to include 

 examples of ' homoplasy ' the whole field is open for what has been styled 

 antithetic alternation, in which the two generations were presumed to be 

 homoplastic. If in the sense of ' homogeny,' then it would be necessary 

 to prove the relation of the somata throughout descent to the nuclear 

 cycle. On the other hand, the term ' antithetic,' while it accentuates 

 the difference between the two somatic phases, is not explicit, in that it 

 dut s not describe the method believed to have been involved in their origin. 

 It would be well to drop these old terms, which are neither exact nor 

 explicit, and to support a more general use of the words ' interpolation 

 theory ' in place of ' antithetic ' and ' transformation theory ' in place of 

 ' homologous.' These words accord better with current views, and are 

 explicit. 



1926. 



From the time that the periodic reduction of chromosomes was recog- 

 nised as general in organisms showing sexuality, the nuclear cycle has 

 formed a natural foundation for the comparison of the life-histories of 

 plants. The normal cycle may be figured to the mind as a closed circular 

 thread with two knots upon it, syngamy and reduction. Between those knots 

 beads may be strung, one, or more than one, or none. These represent 

 somatic developments, which are normally diploid between syngamy and 

 reduction, haploid between reduction and a fresh act of syngamy. They 



