Pigott. — Notts on Nothopanax arboreuin. 



607 



Fig. 9. — Longitudinal section (slightly tan- 

 gential) of ovule, showing general effect 

 of the invaginations of ovule-walls. 

 X28. 



integument grows up. and encloses the nucellus while yet an undifferenti- 

 ated mass of cells, leaving the micropyle now long and narrow (fig. 8). 

 The integument where it borders the funicle becomes very closely con- 

 nected with it. The cells are angular, deeper above the nucellus than at 

 the sides. In the young ovule the 

 ir.tegument constitutes a large pro- 

 portion of its size, but when endo- 

 sperm begins to be formed, and the 

 ovule increases greatly in size, the 

 integument becomes thinner, and 

 spreads over the surface of the 

 rapidlv growing ovule. The body 

 of the ovule undergoes many con- 

 tortions, forming invaginations al- 

 ways lined by the integument. The 

 ovule has thus a very large surface 

 area compared to its volume. Two 

 chief and characteristic invaginations 

 correspond to the ridges in the 

 ovary - wall. There are, however, 

 other smaller invaginations with 

 which there seems to be no corre- 

 spondence in the wall of the ovary. 



Soon the micropyle gives the appearance of being plugged up by the in- 

 tegument, though this may be due to an invagination immediately below 

 it. The cells of the integument are small, and, in the young ovule, uniform 

 in size. During development, however, there are seen one or two layers 

 of much larger, thin-walled cells between the ordinary cells of the integu- 

 ment and the nucellus. These are interrupted at the base, and do not 

 extend quite to the micropyle. They form, therefore, a hollow irregular 

 cylinder open at both ends. These cells are irregular in shape. Their 

 origin was not determined (fig. 13). The demands made upon the integu- 

 ment in the growing ovule by the formation of so many invaginations are 

 quite sufficient to explain its rapidly increasing thinness (figs. 12 and 17). 

 In ovules in which endosperm has been fully formed, the integument consists 

 of cells of two kinds — large outer cells, usually one or occasionally two cells 

 deep. These are turgid, and contain a diffuse green colouring-matter. 

 The inner cells are several cells deep, regular in outline, and with dense 

 protoplasmic contents. The large cells before mentioned (fig. 12) render 

 the connection between the integument and endosperm easily severed, 

 and the two can be easily separated under the dissecting-microscope when 

 the endosperm has reached the " milky " stage. The integument in the 

 seed is brown, and consists of a single layer of large cells (fig. 21). When 

 the section is through the floor of an invagination the cells of the integument 

 are seen to be large and regular. In the seed (when it has been removed 

 from the wall of the ovary, which breaks away from the tissue of the 

 receptacle to enclose it) there are seen to be two chief invaginations. 



Nucellus. 



The nucellus consists at first of an undifferentiated mass of cells loosely 

 surrounded by the integument. The next stage obtained in sectioning 

 was the archesporial stage, in which a central cell of the nucellus had divided 



