132 MINNESOTA BOTANICAL STUDIES. 



species the stele of the hypocotyl does not have the typical 

 structure just mentioned, the number and arrangement of vascu- 

 lar bundles being different. Ulmus americana has two xylen: 

 crescents and numerous small phloem bundles ; Broussonetic 

 papyrifera has a root-like structure ; in Catalpa speciosa then 

 are about eight vascular bundles. 



Primary Structure of the Stele of the Epicotyl. In shape the 

 stele of the epicotyl is often originally somewhat hexagonal 

 though, as in the case of the hypocotyl, becoming at length 

 cylindrical. As is well known there are usually from six tc 

 very many vascular bundles. Sometimes the phloem is com- 

 pletely fused into a closed zone even in very young stages. 



Arrangement of Sclerenchyma in the Hypocotyl. The scler- 

 enchyma of the hypocotyl first appears as four masses in the 

 peri cycle in Toxlyon pomiferum, Liriodendron tulipifera, Cer- 

 cis canadensis, Gleditsia triacanthos, Robinia pseudacacia, Ail 

 anthus glandulosa, Vitis cordifolia, Eucalyptus globulus, 7 e- 

 coma radicans and Catalpa speciosa. In the plants just namec 

 this original disposition of the sclerenchyma becomes alterec 

 either by the intercalation of parenchymatous elements in the 

 areas of sclerenchyma or by the development of sclerenchyrm 

 at other points. In the following plants, however, there is 

 practically no change in the sclerenchyma during the first yeai 

 and the four original masses remain to the end of the season 

 Parkinsonia aculeata, Amorpha fruticosa, Ptelea trifoliata, 

 Berchemia racemosa. 



Comparison of the Hypocotyl and Epicotyl -with Refer enct 

 to the Distribution of Sclerenchyma. Commonly the scleren- 

 chyma in the two regions becomes, at the close of the first grow- 

 ing season, equally well developed and similarly arranged. Ex- 

 ceptions to this rule will now be noted. Sclerenchyma is absen 

 from the hypocotyl of Menispermum canadense, Butneria flo- 

 rida and Rhamnus purshiana although present in the epicotyl 

 In Ptelea trifoliata and Berchemia racemosa at the close of the 

 first year there is a greater development of sclerenchyma in the 

 epicotyl than in the hypocotyl. The reverse of this conditior 

 obtains in Celtis occidentalis and Eticalyptus globulus. Onl} 

 scattered sclerenchyma in small amount was recognized ir 

 either region in year-old material of Broussonetia papyrifera^ 

 in Cephalanthus occidentalis a few only of the pericyclic cells 

 of the epicotyl become sclerotic. 



