CHAPTER XVI 



ABNORMALITIES OF THE LIFE-CYCLE 



The investigations of the middle years of the nineteenth century made it 

 for the first time possible to give a consecutive account of the various stages 

 in the life-history of the Higher Cryptogams, and in particular of the Ferns. 

 The spores of Ferns were first recognised experimentally as reproductive 

 organs by Morrison, who raised young plants from them (1699). John Lindsay 

 observed the germination of the spores (1792); but it was Brisseau-Mirbel 

 (1802) who was the first to trace the formation from them of the prothallus, 

 a body which had already been described by Ehrhart (1788). Kaulfuss, in 

 1827, published good drawings of the germinating spore, the prothallus, and 

 the young plant attached to it, and he gave an excellent summary of the 

 literature up to that date. In 1844 Naegeli discovered the antheridia and 

 spermatozoids, while Suminski, in 1848, ascertained the true nature of the 

 archegonium, and its relation to the embryo. But it remained for Hofmeister 

 to put together and to complete the story. In 1849 his description of the 

 germination oi Pilularia appeared, and two years later, in 185 1, he gave to 

 the world his VergleicJicnde Uiitersiichungen, a work which dealt in the most 

 comprehensive way with the life-histories of archegoniate plants generally. 

 Eight years later Darwin's Origin of Species was published, and " the Theory 

 of Descent had only to accept what genetic morphology had actually brought 

 into view " (Sachs). At first no morphological or physiological history was 

 traced in the facts of the individual life. But gradually it became apparent 

 that an interpretation of the life-history in terms of evolutionary history 

 was possible, and in recent years such interpretations have been the subject 

 of frequent discussion. 



The life-history of a Fern, as described in Chapter i, is held to be that 

 which is normal for the Filicales, because it is usual for the large majority 

 of them, and also for Archegoniatae generally. It is, however, liable to 

 modifications not only in the form and structure of the plants concerned, 

 but also in the several steps observed. Extra stages may be interpolated 

 in the simple cycle, or phases held to be essential may be entirely omitted 

 in the single life. These irregularities often raise questions of the utmost 

 importance morphologically and physiologically; they may even be held to 

 affect views relating to the Descent of the Filicales, and to influence pro- 

 foundly the interpretation of their life-history as illuminating the Descent 

 of plants generally. It is therefore necessary to examine and to estimate at 



