XVI] 



CRESTED VARIETIES 



333 



Three examples are shown in Fig. 307. In (^) the forking is slightly unequal, 

 the stronger shank being to the left. There is a regular alternation of the 

 veins forming the dichopodial midrib, and the whole supply to the smaller 

 right-hand lobe may be held to represent one of those veins which has 

 developed more strongly, and branched more frequently to supply the 

 marginal outgrowth. On this view it would represent a partial reversion 

 from the inequality of the forking in the sympodium towards the primitive 

 equality seen in the juvenile leaves. (Compare Chapter V, Fig. 80.) A similar 

 interpretation would apply to (B). Such conditions harmonise readily with 

 that in {C), where the veins of the two lobes are very equally developed, so 

 that it is difficult to say whether the one lobe or the other is the apex of the 

 dichopodium. In other words, the dichopodium has reverted very perfectly 

 to the primitive, equal dichotomy. 



Fig. 307. Apices of pinnules of Osmunda regalis, var. cristata, showing various states 

 of furcation of the apex. ( x 4.) 



It cannot escape notice that two of the Ferns quoted earlier in this 

 Chapter as showing irregularities of the chromosome-cycle are " crested " 

 varieties. Scolopendrium vulgare, var. crispuni Drumniondiae has been seen 

 to be diploid throughout its life-cycle, while there is strong probability that 

 the converse holds for the Fern styled Lastraea pseudo-mas, var. cristata 

 (= Nephrodium Filix-inas, var. cristatuin), which is presumably haploid. The 

 cresting appears in the juvenile leaves of the apogamously-produced plants 

 of the latter, and examples of their pinnae may be seriated so as to show 

 progressively gradual steps from the normal (Fig. 306, y^) to pronouncedly 

 crested tips (Fig. 306, C). Such facts suggest that some relation exists be- 

 tween the crested state and sexual irregularity. A crested state may be, like 

 apospory and apogamy, in some way the expression of an incompatibility 

 of chromosome-number in synaptic pairing, consequent on the promiscuous 

 hybridisation which is always possible in Ferns. The necessary facts are 

 not yet available for establishing the suggested relation : but so far as they 



