Butters: seeds and seedling of caulopiiyllum. 



29 



Text Figure 4. Diagrams illustrating the structure of the hypocotyl 

 after growth of the epicotyl has taken place. X 15. The letters correspond 

 with those in text fig. 3 



By the time that the protoxylem is well developed in the cotyled- 

 onary bundles throughout the hypocotyl, differentiation of vascu- 

 lar tissue begins to occur in connection with the slowly developing 

 epicotyl. A ring of small celled meristem surrounding a small pith 

 develops in the epicotyl, and extends down into the upper part of 

 the hypocotyl. A little lower, this ring becomes elliptical, and then 

 separates into two parts with gaps opposite the median bundles 

 of the cotyledons. Downward the half ellipses of plerome tissue 

 pass out farther from the center, and break up into strands which 

 stand just inside of the gaps in the ring of cotyledonary bundles. 

 The end strands of each half ellipse may join the meristem tissue 

 in the middle of the corresponding median cotyledonary bundle 

 (d). All the other epicotylary strands, with a single exception, end 

 blindly about the level where the cotyledonary bundles begin to 



