84 MINNESOTA BOTANICAL STUDIES. 



General Observations on the Facts Recorded in the 

 Preceding Pages. 



Without any attempt at ecological explanations of the phe- 

 nomena of the growth and development of seedlings such as 

 given by Goebel* a few generalizations may be made from the 

 plants at present examined. Some of the features to which at- 

 tention is called have been previously discussed by Klebsf and 

 Lubbock^ so that what follows will not be so much a considera- 

 tion of such points but rather a classification of the plants 

 studied with regard to their special peculiarities. 



A knowledge of the shape and general structure of the coty- 

 ledons does not help one to predict the character of the foliage 

 leaves. Sometimes there is a certain resemblance between coty- 

 ledons and the first foliage leaves or even the later ones. The 

 resemblance is, however, chiefly in cases where the cotyledons 

 are ovate or oblong. This is a very common form for foliage 

 leaves as well. Thus in Toxylon -poniifei'uin and Cephalanthus 

 occidentalis the cotyledons and foliage leaves are much alike. 

 That the two kinds of leaves are of the same general shape, 

 may be a mere coincidence and of no great significance. 



Where the general shape of cotyledons and first foliage leaves 

 is much the same, the former may have entire margins and the 

 latter be variously toothed or lobed, e. g., Vitis cordifolia^ Ptelea 

 trifoliata. While, as has been said, there is no absolute agree- 

 ment in the shape of cotyledons in a given genus or family, 

 nevertheless, there are, as is well known, many families in 

 which certain types of cotyledons prevail. The first foliage 

 leaves, however, are more frequently alike, e. g:, Acer spp. 



In cases where leaves of old plants are pinnately compound 

 the first few foliage leaves are often simple, e. g., Acer negundo, 

 Amor-pha spp., Ptelea trifoliata^ Schinus ■Jiiolle, Robinia -pseuda- 

 cacia, Sambucus spp. In all these cases the transition to the 

 compound form is gradual. Thus in Ptelea trifoliata the first 

 leaf is simple, the second leaf usually has but one lateral leaf- 

 let. In Robinia -pseudacacia the second leaf is trifoliate while 

 later leaves are more and more multifoliate. ^ 



Occasionally even the first foliage leaf is compound, as in 



* Organographie dei Pflanzen, 1898. 



t Beitrage zur Morph. und Biol, der Keimung. Pfeffer's Untersuchungen aus 

 dem Botan. Inst, zu Tubingen i: 536. 1885. 

 J Op. cit. 



