320 SCIENCE PROGRESS. 



it had been employed by Steenstrup. He, however, dis- 

 cusses at considerable length the life history of mosses and 

 ferns, in which fertilisation is regarded as falling in the 

 middle of the cycle of development, "becoming the means 

 of transition from a lower to a higher stage of the meta- 

 morphosis ". In a work 1 published two years later similar 

 views with regard to the importance of this alternation of 

 shoots are elaborated in detail ; the importance of the sexual 

 or asexual mode of reproduction is, however, recognised, 

 though the cryptogams are intentionally left out of con- 

 sideration. 



But in the Vergleichende Untersuchungen 2 the life 

 histories of the main groups of archegoniate plants were 

 described in detail and treated comparatively ; from this 

 time the importance of the regular alternation of a sexual 

 and spore-bearing generation has been beyond question. 

 In this work, and even in the Higher Cryptogamia " 3 

 published in 1862, Hofmeister made no remarks on the 

 nature of the alternation of generations, the essential unity 

 of which throughout Bryophytes, Pteridophytes and Gym- 

 nosperms he clearly demonstrated ; neither did he extend 

 the comparison to Thallophytes. 



In the interval between these two works of Hofmeister 

 the materials for this comparison had accumulated as the 

 life histories of the Algae became accurately known. In 

 1856 Pringsheim had pointed out that QLdogonium and 

 Coleochcete, in both of which the zygote divides into a num- 

 ber of cells, approached the level of development of the 

 moss, and had compared the many celled fruits of the latter 

 genus with the sporogonium of Riccia? This view is still 

 further developed in later papers 5 and an important distinc- 

 tion is drawn between the alternation of shoots and true 

 alternation of generations, the succession of individuals by 

 asexual reproduction in Coleochcete being regarded as the 

 equivalent of the former. " We see in the Coleochcetece, 

 just as in the pleurocarpic mosses, the succession of 

 shoots or succession of generations along with the form 



1 Braun(2). 2 Hofmeister (1). * Ibid. (2). 



4 Pringsheim (1). 5 Ibid. (2), (3). • 



