( 825 ) 



outer one arises first and liere we find the first deviation e 



normal course of development in Angiosperms. This integument 

 sinijdy arises as an annulai' fold on the nucellus, with which it 

 remains connected bv the chalaza, while for the rest it grows round 

 pretty loosely. Finally there remains at the point, where its borders 

 meet, a very narrow micropyle, which can oidy be seen properly 

 in truly medial sections. 



After the outer integument has already surrounded half the ovule, 

 the inner one begins to develop. Cell divisions are seen to occur in 

 a few epidermal cells of the nucellus, immediately above the point 

 of attachment of the outer integument. These divisions take place in 

 such a manner, that a wall arises in one of the basal cells of each 

 longitudinal row of the epidermis ; this wall forms an angle of 45° 

 with the longitudinal direction of the ovule, so that each of the cells 

 is divided into two. The upper half remains an epidermal cell of (he 

 nucellus, while the lower half develops to form the inner integument. 

 In a transverse section the number of epidermal cells, counted on the 

 periphery, is seen to be 5, occasionally 6 or 7. At first the inner 

 integument will therefore show in transverse section an equal number 

 of cells. Dividing walls soon arise, however, which make this inner 

 integument two cells thick. More than two layers do not develop, as 

 no further tangential walls are formed, but other walls, both radial 

 and transvei'se to the long axis of the ovule are developed. Especially 

 the number of radial walls is very diiferent in the two cell layers; 

 it is large in the outer layer, but on the other hand small in the 

 inner layer. As a result, the number of cells of the inner layer of 

 the inner integument is generally little more than five, when counted 

 in transverse section. When afterwards the cells of the inner intetiu- 

 ment increase in size and often acquire dimensions, which make 

 them very noticeable, it is the inner cells which are especially large. 

 This growth is often accompanied by strong thickening of the walls. 



The transverse walls, which arise in the cells of the inner integu- 

 ment, enable the latter to grow longitudinally. In this process the 

 top of the nucellus remains free however, and is only surrounded 

 by the outer integument, so that it lies in the endostomium ; the 

 strong longitudinal growth of the inner iidegument is chiefly directed 

 downwards. At its base, near the chalaza, it of course remains 

 connected with the nucellar tissue. 



Now it is very remarkable, that the luiccllar tissue does not par- 

 ticipate by cell division in this strong longitudinal growth of the 

 ovule. The portion of the Jiucellus, which projects beyond the inner 

 integument, remains unaltered, except for cei'tain changes, which 



