XVI] CRESTED VARIETIES 331 



until the relations between certain Archegoniatae with certain definite 

 Thallophytic types have been drawn much closer than the facts at present 

 available would justify. Moreover homoplasy is written so large across the 

 face of the Vegetable Kingdom, and in particular of the lower organisms, 

 that it should give pause to rash speculation. It should suggest caution in 

 recognising as truly phyletic such similarities, whether of somatic develop- 

 ment or of the various life-histories, as have been based upon an obligatory 

 chromosome-cycle. Whatever further interest the normal alternation or its 

 abnormalities seen in the life-cycle of Ferns may ultimately present for 

 comparison with that more lax alternation seen in the Thallophytes, such 

 features cannot yet be profitably used in phyletic discussion. In point of 

 fact, after all the intensive study which has been devoted to the chromosome- 

 cycle of the Filicales, and of the Archegoniatae at large, the question of the 

 origin of alternation in them stands at the moment very much as it stood 

 in 1890, before the cytological difference of the alternating generations had 

 been recognised. 



Crested Varieties 



There yet remain certain abnormalities frequently seen in Ferns of 

 very various affinity, which are described as " crested." In these the leaves 

 are in greater or less degree marked by extra branchings, chiefly at or near 

 to the distal end of the phyllopodium, pinnae, or pinnules. Often the 

 branchings appear as very exact bifurcations, and may even differ in this 

 mode of branching from that seen in the normal parts of the same leaf. 

 Though the distal regions of the leaves are most commonly affected, the 

 forking may appear sometimes in the lower regions of the leaf Scolopendrimn 

 often shows its blade forked into two almost equal shanks. The same is not 

 uncommon in Polypodium viilgm'e, while in certain strains of Nephrodiujn 

 molleXhe leaf frequently appears to fork near to its base, giving the semblance 

 of two equal leaves borne upon a single stalk (Fig. 305, B). In cultures grown 

 in Glasgow from spores this abnormality of N. niolle recurred with some 

 degree of persistence in successive generations. Such simple forkings as 

 those named are frequently combined with extra pinnations beyond those 

 normally present. The result may be complex structures which are difficult to 

 refer back to the exact factors to which they owe their origin (Fig. 305, A). 

 In extreme cases crested Ferns present a very full habit, and are often of 

 great beauty. In particular, the crested forms oi Nephrolepis are raised for 

 the market in large numbers by nursery gardeners as decorative plants. 

 But the extreme types are liable to revert under ordinary conditions of 

 culture towards the normal and less decorative form of leaf 



A very considerable number of British Ferns have been found to show 

 crested varieties. Many are recorded under such names as vars. nmltifida 



