THE OTTAWA NATURALIST 



VOL. XXII. OTTAWA, FEBRUARY, 1909 ' No. 1 1 



OBSERVATIONS ON SEEDLINGS OF NORTH AMERICAN 

 PH^NOGAMOUS PLANTS. 



By Theo. Holm, Brookland, D.C. 



(Continued from page 174). 



In passing to describe some types of dicotyledonous seedlings, 

 it might be stated at once that the majority of these possess 

 epigeic cotyledons. There is, thus, a well marked distinction 

 between the two classes Monocotyledones and Dicotyledones, 

 consisting not only in the number of cotyledons, but also in the 

 structure of these depending upon the different function w'hich 

 they have to perform. We have seen that in very many, really 

 in most of the Monocotyledones the cotyledon has acquired a 

 certain shape and internal structure for absorbing the endospenn, 

 for instance the scutellum in 6'rawnne'(^,and the club-shaped organ 

 in SmilacecB, CommelinacecB, ScitammecB, etc., instead of being 

 developed as a free, assimilating leaf as in Alisma, Agave, 

 Sisyrinchium, etc. Such peculiar modifications of the cotyledon- 

 ary leaves are not known from the Dicotyledones', in these they 

 generally have the same function to perform as the proper leaves, 

 to assimilate, or, sometimes, they are also the bearers of reserve 

 food-substances, and are then either epigeic or hypogeic, especial- 

 ly the latter. Another striking contrast between these two 

 classes is the usually much stronger development of the primary 

 root, and of the hypocotyl in the Dicotyledones. Moreo\-er, these 

 two organs have, in the Dicotyledones, very often acquired a 

 certain structure in accordance with their functions ; for instance 

 the primary root may be developed as a storage root, and the 

 hypocotyl may, sometimes, attain quite a considerable increase 

 in thickness and contain abundant deposits of food material, 

 or its function may simply be to raise the cotyledons above the 

 ground, thus liberating them from the seed-coat. In the 

 Monocotyledones , on the other hand, the primary root seldom 

 persists, and hardly ever as a storage root, and the hypocotvl is 

 seldom developed to any great extent, and shows no modifica- 



