140 ROBERT TRACY JACKSOX ON 



iiiid hear more or less resemblance to the early nepionic leaves of the seedling. Snch is 

 louiid to be the fact in many cases, as Aqnilegia, Fig. 17, Liriodendron, Fig. 12, Aihutf/uis 

 (jiajtdiilosa, Acer, several species. Fig. 29, jVer/mido aceroides freqnently. Fig. 30, Iledera 

 helix, Fig. 44, Tecoiufi rtidicdiis. Fraxinus, several species. Fig. 48, SriKnafras xassafras, 

 •Fig. 51, Hicorhi oratd. Fig. (Jl, C(jcos, I'hoeni.v, Kentia, Areca, ('aryota and many other 

 pinnate ])ahns, Pigs. Kll, 10>;. !l."). !I7. 



If the distal end of the leaf ivpeats ne[)i()iiic characters, then types which hiive com- 

 pound imparipiiniate leaves should have a shnple nepionic leaf, and such is the case in 

 species observed, the exceptions occurring only wlien the first leaves bv accelerated 

 <levelo])ment are trifoliolate [liJuix fo.i-'icodciidroii, i\.\\M\{\n\>^) . ()\\ the same liasis. com- 

 pound paripinnate-leaved types should have compound paripinnate nepionic leaves with 

 two or more leaflets ; sucli is found to be the case in most types (Gleditschia, Fio-. 39) 

 bnt Sesbania, as noted (p. 103), is an exception, having first a shnple nepionic leaf. 



It' the tip of a leaf is the simplest part, then increased complication should take place 

 pi-oximaily. This is obviously the case in all impari[iiiniate leaves. It is markedlv the 

 case in l^tcrh (iqiidhid and many other ferns. In some cases the [>i'oximal portion of the 

 leaf is the simplest. This is n(.)tal)ly the case in (Tijimtix'hidii^ disin/s. Fie. 37 wliere 

 latei-al dixisions are reduced to single leaflets. This simpler or last formed portion is com 

 l)arable to the simple condition of the sucker and probably of the seedling. To compare 

 with ontogenies of whole organisms: adults or later periods of growth are often simpler 

 than the young in degraded animals, as Ostrea, Baculites, parasitic Crustacea. Adult 

 plants may also be simpler than their own j'onng, AvqjeJopfds tricKSj^idata, Fio-s. 20, 22. 

 The tip of the leaf is sometimes the specialized portion, Dionaea, Cohaea scandens. 



If there is ontogenesis of individual leaves, then an}- cause which interfered with 

 such development would tend to produce an imperfect, innnature, primitive, or reversion- 

 ary leaf. Such reversionary, more or less isolated leaves are found in Liriodendron, Am- 

 pcJops'm qnuiquefolUi, N('(jinid() oceroides, Gleddschia /rica/d/ios, Plafaiiiis occidentcdix 

 Hicorifi oi-dtd, Fj-d.riiuis d)nerica)id, F. pithei^cens, and pinnate palms. In such ontoo'enies 

 of in-dividual leaves in degraded species we may expect to find localized evidence of ances- 

 tral moi'c specialized forms. Such occur in the occasional compound leaves of Frd.riinn^ 

 uiioiiidld, which species is characterized by simple leaves. 



In a word, primitive or reversionary features in adult plants mdy be looked for in 

 such localized parts as suckers, weak, senile, or abnormal growths, in the distal and ])rox- 

 imal parts of leaves, or in muisual individual leaves. How general such localized primitive 

 features or stages in development will prove to be, is uncertain. To proAe that they do 

 sometimes exist is all that is attempted here. 



New varieties and species in the state of nature are generally supposed to oritdnate 



