410 MANIPULATION. 



mould, after having been placed but a very short time in 

 water, and the appearance was generally attributed to the 

 first act of growth of the seed, but the microscope shows that 

 it is due to the elongation of membranous cells, by the 

 uncoiling of an elastic spiral fibre contained within them. 

 The same phenomenon has been observed by Mr. Eappist in 

 the seeds of the Acanthodium spicatum, a plant brought from 

 Upper Egypt by Mr. Holroyd ; also in other plants of the 

 family Acanthacea, but the presence of spiral cells is not con- 

 stant throughout the whole family. The entire surface of the 

 seed of the Acanthodium is covered with whitish hairs, which 

 are so compressed as to adhere closely to it in the dry state, 

 being apparently glued together at their extremities. On 

 being placed in water, these hairs are set free, and spread out 

 on all sides, they are then seen to be clusters of from five to 

 twenty spiral cells, which adhere firmly together in their 

 lower portions, while their upper parts are free, separating 

 from the cluster at different heights, and expanding in all 

 directions like plumes, forming a very beautiful microscopic 

 object. The free portions of the cells readily unroll, exhibit- 

 ing the spire, formed of one, two, or occasionally of three 

 fibres, which may sometimes be seen to branch, and not un- 

 frequently break up into rings. Throughout the whole length 

 of the cell, the coils are nearly contiguous ; in the lower part 

 they are united by connecting fibrils, and towards the base 

 of the adherent portion become completely reticulated. The 

 testa is a semi-transparent membrane, formed of nearly regular 

 hexagonal cells, whose centres are occupied by an opaque mass 

 of grumous matter. Those cells which sm-round the bases of 

 the hairs are considerably elongated, and, gradually tapering 

 into transparent tubes, appear to occupy the interior of the 

 spiral clusters. 



Two species of Blepharis are mentioned as possessing a 

 structure very similar to that of Acanthodium spicatum, differ- 

 ing chiefly in the smaller and more uniform diameter of the 

 spiral cells, and in their thicker fibre, which is always single 

 and loosely coiled. 



The seed of Ruellia formosa, on being placed in water. 



