Morphology and Physiology of the Pome Lenticels of Pyrus malus

1. The development of the lenticels of 18 horticultural varieties of apples is traced. Lenticels may be open or closed depending on the character of the hypodermal cells. These may be cutinized or suberized and thus rendered closed to the free movement of gases or liquids. Lenticels may also be closed when the stoma associated with the lenticel is closed over by means of the epidermal cuticle. Lenticels may be open when the hypodermal cells are unmodified or when the modified cells have been torn apart. 2. The total number of lenticels per apple is within certain wide ranges characteristic of the variety. The number may range from 450 to 800 in the case of Winesap apples and from 1500 to 2500 in the case of Spitzenburger apples. 3. The number of lenticels per apple may be varied by varying the amount of water available to the plant during the early development of the apples. This reaction is varietal rather than general. The Winesap apple when given more water produced more lenticels per apple than when grown with less water. The Delicious apples when given more water actually produced fewer lenticels even though the apples were larger. 4. Lenticels may be closed by processes which favor dehydration of the outer tissues of the apple. While the apples are still immature, they respond more completely to such treatment than do mature apples. After apples have been in storage for 6-8 weeks, they respond only after prolonged treatments. 5. Carbon dioxide gas within the apple escapes with equal speed whether the apple has many or few open lenticels. The period necessary for the gas to come to equilibrium with new temperatures is 49 to 52 hours.