1893.] NATURAL SCIENCES OF PHILADELPHIA. 189 



from the under leaf surface only. The upper leaf surface was 

 almost completely hidden from view and consequently protected by 

 means of the peculiar infolding of the leaf in the early stages of its 

 development. The long diameter of the next younger leaf, with its 

 sides similarly rolled in as in the case of the preceding one, meas- 

 ured 1 cm., fig. 1, G, and the thick gelatinous mass which coated 

 it, extended also over the adjoining petioles and the punctum vege- 

 tationis. To the naked eye, this secretion appears as a transparent 

 colorless jelly. Held up to the light it can be observed that numer- 

 ous very fine hair-like processes extend into it from the plant. On 

 magnification, these processes appear as represented in fig. II, A, 

 B, C, D. It becomes at once apparent that these processes belong 

 to the category of trichomes being outgrowths from the epidermis. 

 In spite of the variety of form as represented in fig. II, these 

 trichomes show a certain uniformity of structure. They consist in 

 the main of one large cell, fig. II, X, and of a group of smaller 

 cells uniting the large terminal cell with the epidermis below. Only 

 two of this group of cells are shown in fig. II, A, Y. The trichomes 

 are either unbranched, fig. II, A & B, or else they are branched 

 or rather forked, fig. II, C & D. There cannot be the slightest 

 doubt that these trichomes are the organs which are active in the 

 secretion of the jelly, and they may therefore be termed glandular 

 hairs. Since, at the time of collecting, it has been impossible for me to 

 examine carefully the structure of these glandular hairs, the mater- 

 ial was placed in 50 per cent, alcohol, and the observations which I 

 here record were made entirely on alcohol material. The gelatin- 

 ous coating suffered no perceptible change through this new medium. 

 From a leaf 1 cm. long, a portion of the epidermis of the under 

 leaf surface was removed and examined. The glands were closely 

 crowded, leaving no spaces between them. What I shall call the 

 gland proper is represented in fig. II, A X, plus the group of 

 smaller cells at the base already referred to, and two of which are 

 represented by Y of fig. II, A. The gland of fig. II, A was of 

 about the average size, and measured .205 mm. in height and .0369 

 mm. in width. Surrounding the gland proper will be noticed what 

 I shall in distinction from this and for convenience merely term 

 sheath, fig. II, A. S., which measured, in this particular case .2337 mm. 

 x .0943 mm. The size of the sheaths varies considerably, and the 

 explanation of this variation of size is found in the peculiar signifi- 

 cance of these structures which will be dwelt upon immediately. 



