THE COMMENCEMENT OF THE PHANEROGAMIC FRUIT. 81 



flowering plants we find a definite central mass of cells, the nucellus, surrounded 

 by a well-marked sheath, the coat or integument. Generally the integument is 

 double, as in Delphinium and Butomus (cf. figs. 210 ^' ^' ^°), in other cases it is 

 single, as in Compositse, Umbelliferae, Hippuris and Cycas revoluta (cf. fig. 208^). 

 In most Orchids the nucellus is inclosed in a large-celled, inflated and transparent 

 integument, through which it is distinctly visible (cf. fig. 212^). In not a few 

 epiphytic Orchids, however, this contrast of parts is only imperfectly shown, whilst 

 in the BalanophoresB and various other parasites no trace of the distinction into 

 nucellus and integument is found. In all cases where an integument is present 

 it is discontinuous at one point, where the nucellus is uncovered. This is the 

 micropyle. Sometimes the micropyle is at the apex of the ovule, but in a very 

 large number of cases the whole ovule is bent over so that the micropyle is situated 

 close to the point of attachment of the ovule. The ovule may be attached to its 

 support (placenta) by means of a filamentous cord, or it may be directly seated upon 

 it. The common condition of an inverted ovule fused with its filamentous stalk is 

 shown in figs. 208^ and 210^*'. The filamentous stalk is technically known as 

 the funicle, and the ridge where it is fused with the ovule as the rajihe (cf. vol i. 

 p. 644). 



The cells of the nucellus of the ovule show a very unequal growth. One of 

 them enlarges in a conspicuous manner, and is known as the Embryo-sac. In 

 Conifers it attains relatively to the other cells of the nucellus enormous dimensions, 

 whilst in most other flowering plants as it grows it encroaches upon the other cells 

 of the nucellus till only a single layer remains surrounding it. And even this layer 

 may be in part absorbed, so that the embryo-sac actually penetrates to the 

 micropyle. The protoplasmic contents of the embryo-sac is richly vacuolated, but 

 at the end directed towards the micropyle vacuoles are absent, and the protoplasm 

 breaks up into several distinct protoplasts, each of which is provided with a con- 

 spicuous nucleus but in the first instance with no cell-membrane. As a rule three 

 such protoplasts are found at the micropylar end of the embryo-sac; of these one 

 only gives rise, after fertilization, to an embryo. This cell is the ooplast or "ger- 

 minal vesicle", the other two are named synergidce (cf. also, figs. 315 and 316). 



In the ovaries of Orchids, as shown in figs. 212^'2'3>*, the ovules arise in great 

 numbers upon peculiar furrowed ridges of the carpels. They arise from the super- 

 ficial cells of these ridges, and are not provided with any vascular-bundle connec- 

 tions; in fact, they are comparable to those epidermal structures known as hairs or 

 trichomes. This analogy is emphasized by the fact that in the ovaries of many 

 Orchids real hairs are present, as, for instance, in Loelia Perrinii and Coslogyne 

 plantaginea, transverse sections of which are represented in figs. 212^-2.3,4. j^ 

 these remarkable species six ridges project from the wall into the ovarian cavity, 

 and from all of these hair-like structures are developed. The three ridges belong- 

 ing to the curious excavated receptacle, already described, alone bear ordinary 

 anicellular hairs, the others bear ovules, one of which is shown in fig. 212^. 



The ovules of Cycads are very differently developed, as may be seen from a 



