LECT. IX.] HYBERNACULA GEMS. 475 



thick, opaque, and covering the whole of the 

 terminal shoot above the insertion d. of the 

 last evolved leaf, the footstalk of which b. is pur- 

 posely left in the figure : in fig. 2, the sheath is re- 

 moved to display the leaf a. seated on its footstalk 

 e. and wrapped round the sheath of the next ex- 

 pected leaf. In other instances this sheath is thin, 

 semi-transparent, and filled with a gelatinous 

 matter, which involves the young leaf; as exem- 

 plified in the Dock tribe, Riimex. These sheaths or 

 utricular coverings cannot be regarded as hyber- 

 nacula, as they are present in every season of the 

 year; but, inasmuch as they preserve the young leaf 

 from the stimulus of light and the effects of mois- 

 ture, they bear a close analogy to the hybernacu- 

 lar scales. Their chief use, however, is to re- 

 strain the perspiration of the young leaf, till such 

 time as its vessels are sufficiently perfect to supply 

 by absorption the exhaustion of moisture which 

 that function necessarily occasions. 



The origin of the gem has been already suffi- 

 ciently investigated (p. 383-406). It is evidently 

 nourished during the summer by the leaf, which 

 is, perhaps, to the embryo in the gem, what the 

 flower is to the fruit * ; but when the leaf falls, the 

 gem is left to its own resources; and scarcely any 

 visible change occurs in its aspect or its magnitude 



* " La feuille est au bourgeon ce que la fleur est au fruit 

 " et a la graine. " Essais sur la Veg. par A. Aubert du Petit- 

 Thouars, p. 14-5. 



