LOCALIZED STAGES IN DEVELOPMENT. 139 



by acceleration of development. An example of acceleration is Iihns toxicodendron. 

 (PI. Ifi, fig. 18) in wliicli the nepionic leaves are as complex as in the adnlt, though 

 most species of the genus have simple nepionic leaves. Another case is Ampelopsis tricu- 

 spidata in which the nepionic leaves (PI. 17, lig. 20) are trifoliolate, whereas the leaves 

 of the adult are unifoliolate. In the allied species, ^1. quinquefoUa (PL 16, fig. 1!)), the 

 nepionic leaves are trifoliolate but adult leaves are palmately five-foliolate. 



Leaves of suckers or branches f)-om the base of the plant, or from the root, frequently 

 repeat the form of nepionic leaves so closely that such may be considered localized i'e\er- 

 sionary stages. Such reversionary leaves from the base of plants are seen in AihiiilJiiix 

 (jlandulosa, Fig. 14, Ampjclopsix irivuxpUJnta, Figs. 2o, 25, Necjundo aceroidcs. Fig. o5, 

 Fatda jap>onk-a, Fig. 42, Tecoma radlcam, Fraxinus americana, Fig. 47, Sm^sfifrm msm- 

 fras, Hicoria ovata, Fig. CO, PJatanm^ occideutaHs, Figs. 55, 56, Quercns, several species. 

 Figs. 63, 65, 69, 70, Pinus rUjlda, Fig. 77, Paphisj!(d}eIUforiiiis, and Arecn htfescois. 



While suckers repeat nepionic characters, they are often highly accelerated in their 

 devektpment, so that only one or two, or a few, leaves at the base are reversionary. Also 

 there may be considerable diti'erence in the degree of reversion in individual suckers, ;is 

 in the Trumpet Vine, White Ash, and Black Oak, Figs. 69, 70. Suckers may i)resent more 

 primitive characters than the seedling, as A'ddiifJui^^ (jhmduloxd, Fig. 14, in which the first 

 leaves are simpler than the first nepionic leaves of the seedling. As far as observed tb.is 

 is miusual. 



Considerable variation often occurs in suckers, as noted in the White Ash, Black Oak, 

 and Aiiauthus. While this is more or less confusing in attempting to correlate sucker 

 growth with nepionic and ancestral characters, it is not more so than tlie variations often 

 found in seedlings, as especially noted in the cases of Thuija ocvhh-utalts and Libocednis 

 deciirrens (p. 119, 122) . 



Reversionary or localized stages are marked features of aljuormal growths, as "birds- 

 nest" growths of the Hed Cedar, Fig. 8, p. 117, suckers of the Pitch Pine, Fig. 77. 

 They are frequent in vigorous growtlis, as terminal shoots of the Red Cedar, Fig. 7, page 

 117, and Red Maple and Pfdtaiius occidental^, Fig. 58. Reversionary features also 

 often occur in feeble or retarded growths, as seen in growths formed late in the season, 

 or on injured branches. Tulip-tree, Ailanthus, Acer ritbnim, A. jjeiuisj/lrniiicuiu, A. spica- 

 tum, the White Ash and Red Ash. They may occur in sickly or old age growths, as in 

 the Red Cedar. 



It seems that the leaf itself has an ontogenesis repeating more or less fulh" tlie ontog- 

 eny of the young. In the development of the leaf the distal part is usually formed 

 first, and during growth the proximal partsare progressively added. If this is true, wt' siiould 

 expect to find that the distal ])art of the leaf woidd be the simplest, most primitive part. 



