134 MINNESOTA BOTANICAL STUDIES. 



the endodermis is more distinct and persists for a greater length 

 of time, the pith is smaller, sclerenchyma is often less well-de- 

 veloped and differently arranged and a hypoderma, so common 

 in the epicotyl, is nearly always absent. Cork formation in 

 the hypocotyl begins either in the same cell-layer that it does 

 in the epicotyl or in a deeper layer, never in a more superficial 

 one. 



Starch is, as a rule, distributed in the same way in both 

 regions. It is usually present in the endodermis in the early 

 stages but does not appear in other tissues until the plant has 

 developed foliage leaves, in considerable number. 



As to the structure of the stele it may be said that in the 

 hypocotyl there are usually four primary vascular bundles. 

 The exact disposition of the phloem and xylem elements is 

 subject to some variation. Occasionally there are more than 

 four bundles. In the epicotyl the vascular bundles are from 

 six to eight or very many. 



The hypocotyl does not have a root-like structure. 



EXPLANATION OF PLATES. 



Plate V. Drawings of cross sections to show the primary stelar 

 structure of the hypocotyl of Ulmus americana, Celtis occidentalism 

 1 ' oxylon pomiferum and Broussonetia papyrifera. 



Plate VI. Drawings of cross sections to show the primary stelar 

 structure of the hypocotyl of Menispermum canadense, Butneria 

 florida, Amorpha fruticosa, Robinia pseudacacia and Ptelea tri- 

 foliata. 



Plate VII. Drawings of cross sections to show the primary stelar 

 structure of the hypocotyl of Ailanthus glandulosa, Schinus molle, 

 Berchemia racemosa, Eucalyptus globulus, Catalpa speciosa and 

 Cephalanthus occidentalis. 



Plate VIII. Photographs of cross sections to show the primary 

 structure of the hypocotyl. I. Ulmus americana, 2. Liriodendron 

 tulipifera, 3. Parkinsonia aculeata, 4. Cercis canadensis, 5- 

 Berchemia racemosa, 6. Vitis cordifolia, *]. Eucalyptus globtdus, 

 8. Tecoma radicans. 



The drawings were all outlined with the aid of a camera lucida. 

 The magnification used was about five hundred diameters. For pub- 

 lication the drawings have been reduced to one-half their original size. 

 The magnification used in making the photographs was from fifty to 

 eighty diameters. They have been slightly reduced. All drawings 

 and photographs were made by the author from his own preparations. 



