NOTES. 
THE DEVELOPMENT OF THE SEED-COAT OF CARICA PAPAYA.'— 
The seed-coat of many species of Carica shows a complicated structure, the highest 
degree of differentiation being reached in the seeds of C. microcarpa , C. hastaefolia , 
and C. Papaya (the Paupauw). Klebs 2 has described the constitution of the mature 
seed-coat in the two former species, but has not followed up its development from the 
unfertilized ovule—a development which in the case of C. Papaya shows points of 
interest. Material of the fruit and seeds of this species, at various stages before and 
after fertilization, was obtained in Angola during the recent Percy Sladen Memorial 
Expedition by Dr. H. H. W. Pearson, who handed it over to me for examination. 
The fruit of C. Papaya is a one-celled berry, with seeds lining the wall. These 
seeds, when mature, are oval in form and about 8 mm. long. Their coat consists of 
two separable layers—a hard reddish-brown endotesta, covered by a soft white sarco- 
testa. s The endotesta rises into irregular ridge-like outgrowths, which run down the 
length of the seed (Fig. i, a) and appear in transverse section as pyramidal projec¬ 
tions (Fig. i, b). The sarcotesta fills up the hollows between these ridges, so that the 
surface of the seed, while still enclosed within the fruit, is smooth and shiny; but 
when it is set free, the sarcotesta quickly loses its watery contents and shrivels down 
into the hollows. 
In the young ovule, the two integuments develop as usual, and at the time 
of pollination consist each of four or five layers of ordinary parenchyma (Fig. 2). 
Immediately after pollination, these layers begin to show the following series of 
changes:— 
A. The inner integmnent. 
The cells of the inner epidermis (a) are the only ones in this integument which 
retain their original form. As the seed matures, they enlarge, and a cuticular layer 
is formed on the outer side where they are in contact with the nucellus. At the same 
time, tannin is deposited in their cytoplasm, so that the contents of each cell become 
converted into a tanniferous block (Fig. 4). All the other cells in the integument 
begin to show sliding growth immediately after pollination (Fig. 3), the cells of the 
outer epidermis (h) elongating in a direction parallel to the long axis of the seed, while 
those of the underlying layers lengthen tangentially. Their walls become thickened 
1 Percy Sladen Memorial Expedition in S.W. Africa, 1908-1909; Report No. 3. 
2 Klebs : Beitrage zur Morphologie und Biologie der Keimung. 
3 This sarcotesta was formerly described as an arillus (Baillon : Natural History of Plants, 
iv, 293, London, 1880). 
[Annals of Botany, Vol. XXIV. No. XCV. July, 1910.] 
