86 Mutations and Evolution. 



in the male gametophyte of many Gymnosperms. There is one 

 such cell in Cycads, which persists. Ginkgo has one ephemeral 

 and one persistent prothallial cell which are cut off in succession 

 by the side of the microspore, while in Pinus both prothailial cells 

 dwindle promptly to small dark-staining masses, as though the life 

 had quickly gone out of them. The nucleus may begin to dis- 

 organize even before the cell-plate is formed. Such structures 

 represent momentary stages of an ebbing tide. In Picea canadensis, 

 Hutchinson (1915) has found all these and other conditions to occur 

 as variations. 



Recapitulation in the Sporophyte. 



If now we turn to the sporophyte, we find again many of the 

 most striking cases of recapitulation in Gymnosperms. Indeed they 

 appear to be of more frequent occurrence in this group than in any 

 other plants. A possible reason for this has already been suggested, 

 namely the relative infrequency of mutations. It is well to keep in 

 mind also that recapitulation in the sporophyte usually indicates 

 adaptation to altered conditions. Among well known instances in 

 Conifers may be cited the genus Phyllocladus, characterized by an 

 absence of leaves, the branches forming flattened leaf-like expansions. 

 The seedlings, however, have a terete axis bearing ordinary leaves 

 and this obviously represents the ancestral condition, from which 

 for some unknown reason the genus departed. That such an 

 alteration is not mutational is indicated, according to the present 

 interpretation, by the fact that the ancestral condition is thus clearly 

 present in the earlier stages of ontogeny. A mutational change, being 

 represented in every nucleus from the fertilized egg onwards 

 would have eliminated, or rather transformed, this juvenile stage. 

 In CEnothera, as de Vries (1909) pointed out, the first leaves after 

 the cotyledons make it possible to recognize a mutant form. 



To mention threeothercases of recapitulation in Gymnosperms: 

 A feature of the genus Pinus is the occurrence of dwarf shoots, 

 each bearing a fascicle of needle leaves. But in the seedling the 

 leaves are scattered on the stem as in other conifers. Similarly 

 the genus Larix, unlike most conifers, has deciduous leaves ; but in 

 the juvenile stage the leaves adhere for several years. In the 

 Mariposa grove near the Yosemite valley in California I observed 

 that Sequoia gigantea is a number of years old and many feet high 

 before its foliage acquires the characteristic appressed form. When 

 grown in the English climate, this appressed type of foliage appears 

 never to be quite reached even in old trees. 



