21 



the seed, by cutting the umbilical hands^ it 

 died, though the root was perhaps twice the 

 length of the plant ; yet when the seeds 

 remained attached to the plants till the 

 roots had become woody, the plants grew 

 for years. I imagine that the elabora- 

 tion of the sap is entirely in the seed, 

 and passes through the umbilical bands, 

 for the growth of the plant upward and 

 of the root downward. These umbilical 

 bands pass one to each cotyledon of the 

 seed, in dycotyledonous plants. They may 

 be considered as the stalks or petioles of 

 leaves ; and in reference to a theory of 

 Priestly's, that plants derive their nutri- 

 ment from the air through the medium 

 of their leaves, it may be stated that the 

 cotyledons themselves may be considered 

 as leaves, and indeed in many plants 

 actually become what is called hypogeal, 

 that is, they rise above the earth into the 

 air, and are converted into what are called 

 B 3 



