CHAP.V.] the Influence oftJie Knoivlcdge of Cryptogams. 203 



task to submit the different forms of the Muscineae, the 

 Vascular Cryptogams, and the Gymnosperms to exact inves- 

 tigation in order to ascertain all the details in the process 

 of development in these plants, the formation of the embryo, 

 the succession of cells at the apex, the first appearance and 

 further growth of the lateral organs ; and the more careful the 

 observation, the more clearly even to its farthest results does 

 the correctness of the alternation of generations asserted by 

 Hofmeister everywhere appear. It does not fall within the 

 limit of this history to pursue the subject further, and to show 

 how the doctrine of alternation of generations and the know- 

 ledge of the morphology of the Cryptogams were further 

 advanced by later and distinguished researches, such as those 

 of Cramer on the Equisetaceae, of Pringsheim on Salvinia 

 (1862), of Nageli and Leitgeb on the formation of roots in the 

 Cryptogams, of Hanstein on the germination of the Rhizo- 

 carps, and of others. 



THALLOPHYTES. 



The method of investigation which starts from the first steps 

 towards the formation of the embryo before and after fertilisa- 

 tion, and follows the advancing segmentation and growth through 

 all the stages of development up to the final completion of the 

 embryo-plant, has led since 1850 in the case of the Muscineae, 

 Vascular Cryptogams, and Phanerogams to great certainty in 

 the morphological explanation of the organs, while the deter- 

 mination of affinities has ceased to be arbitrary and insecure ; 

 the way was now known which would lead to the desired end, 

 whenever it was sought to establish the affinities of a genus of 

 Cryptogams or of the larger groups of Phanerogams ; the day 

 of ingenious guessing and trying was over ; the only plan was 

 patient investigation, and this always yielded a result of lasting 

 value. 



The case was quite different with the Thallophytes still in 



