572 PARASITISM OP NOTOTHIXOS INCANUS VAE. SUBAUREUS, 



Underlying the epidermis is a zone of several layers of thin-walled paren- 

 chymatous cells, many of which contain chlorophyll granules. These cells have 

 thin cellulose walls. Traversing the centre of this zone is a narrow tracheal 

 region, consisting of a single series of tracheae with cambiform cells on either 

 side (/.c.) ; this zone is the fruit coat, composed of the ovary wall and the con- 

 tinuation of the receptacle. Within this zone is a broad region composed of 

 three distinct layers, probably representing the integ-ument and nucellus of the 

 seed, namely: on the outside, one or two layers of small, thin-walled parenchyma 

 cells; in the middle, a single layer of broad gelatinous cells with thick gelatinous 

 walls, little protoplasm and large nucleus. This layer is the important one in 

 bringing about the swelling and subsequent rupture of the fruit. Underlying this 

 gelatinous layer there occur several rows of elongated cells, with a distinct row 

 of tracheae in the centre. The gelatinous layer is attached on its inner side to 

 this tissue and on its outer to the small-celled layer. The seed-covering is clearly 

 seen in Test-fig. 1, p.Z. representing the parenchymatous layer, g.l. the broad 

 gelatinous layer and Tr.l. the inner traeheal-bearing layer. The gelatinous layer 

 is barrel-shaped and open at both ends. The next tissue met with on passing 

 inwards, is the endosperm (end), thin-walled, filled with starch grains and sur- 

 rounded by a distinct, small-celled, large-nucleated, peripheral layer. At the 

 upper end of this endosperm the large embryo is situated {emh.). The endos- 

 perm cells surrounding the root of the embryo are small and compact, and form 

 a sheath aroimd it, which looks very much like a root-cap. On germination, 

 however, the root grows through this sheath. 



The fruit coat is prolonged upwards into a short style and stigma (si), 

 the cells of which are papillate. At the base of the fruit there is a mass of 

 short reticulately and spirally thickened tracheae embedded in a region of small 

 thin-walled parenchyma cells. Sieve-tubes are not present, as far as I could de- 

 termine. This basal region represents a mechanically weak one, and it is here 

 that the fruit separates from the stalk (Test-fig. 1, deh.). 



In regard to the mechanics of seed dispersal, it is readily seen that the 

 motor-tissue is the gelatinous cells almost surrounding the fruit, whUe the 

 dehiscence occurs at the base. The gelatinous cells are not aU arranged in the 

 same manner. In the upper portion of the fruit they are practically at right 

 angles to its long axis, while in the lower portion, they are obliquely inclined 

 to this long axis. When swelling takes place, on absorption of water, or when 

 reduced transpiration increases the turgeseence of the fruit, obviously the gela- 

 tinous cells will swell differently and, therefore, tension will develop in the fruit. 

 The lower gelatinous cells have thinner walls than the upper, which will swell 

 more than the lower, and therefore the upper part of the fruit will become more 

 distended than the lower. The dehiscent la.yer is at the base, where there is a 

 line of mechanical weakness. When conditions are favourable, i.e., when there is 

 sufficient humidity and reduced transpiration, the gelatinous cells swell in different 

 degrees and directions, and the severance of the fruit from the stalk occurs. Im- 

 pact of the fruit against any object will cause the gelatinous-covered seed to be 

 extruded, but this would occur automatically by the pressure developed in the 

 upper portion of the fruit. The swelling of the gelatinous cells undoubtedly 

 takes place by the walls absorbing water, and not by the osmotic activity of the 

 cell contents. 

 The Seed. 



In Notothixos the endosperm with its embryo is surrounded by a gelatinous 

 region, which is differentiated into the three zones mentioned above. These three 



