426 STRUCTURE OF PETALS AND ANTHERS. 



lamp, after which it is to be covered with a thin glass. The 

 boiling ' blisters ' it, but does not remove the colour ; and on 

 examination many of the Cells will be found showing the mam- 

 milla very distinctly, with a score of hairs surrounding its base, 

 each of these slightly curved, and pointing towards the apex of the 

 mammilla. — The Petal of the common Scarlet Pimpernel (Anagallis 

 arvensis), that of the common Chickweed (Stellaria media), to- 

 gether with many others of a small and delicate character, are 

 also very beautiful microscopic objects ; and the two just named 

 are peculiarly favourable subjects for the examination of the Spiral 

 Vessels in their natural position. For the Veins which traverse 

 these petals are entirely made-up of Spiral Vessels, none of which 

 individually attain any great length ; but one follows or takes the 

 place of another, the conical commencement of each somewhat 

 overlapping the like termination of its predecessor ; and where 

 the Veins seem to branch, this does not happen by the bifurcation 

 of a Spiral Vessel, but by the ' splicing-on ' (so to speak) of one to 

 the side of another, or by the ' splicing-on ' of two new vessels 

 diverging from one another, to the end of that which formed the 

 principal vein. * 



317. The Anthers and Pollen -grains, also, present numerous 

 objects of great interest, both to the scientific Botanist and to the 

 amateur Microscopist. In the first place, they afford a good oppor- 

 tunity of studying that form of ' free ' Cell-development, which 

 seems peculiar to the parts concerned in the Reproductive process, 

 and which consists in the development of a new Cell-wall round 

 an isolated mass of Protoplasm forming part of the contents of a 

 'parent-cell;' so that the new Cell lies free within its cavity, 

 instead of being developed in continuity with it, as in the ordinary 

 methods of multiplication (§ 2-49). If the Anther be examined 

 by thin sections at an early stage of its development within the 

 young flower-bud, it will be found to be made-up of ordinary 

 Cellular Parenchyma in which no peculiarity anywhere shows 

 itself : but a gradual ' differentiation ' speedily takes-place, con- 

 sisting in the development of a set of very large Cells in two 

 vertical rows, which occupy the place of the Loculi or Pollen 

 Chambers that afterwards present themselves ; and these Cells 

 give origin to the Pollen-Grains, whilst the ordinary Parenchyma 

 remains to form the walls of the Pollen-Chambers. The first 

 change consists in the multiplication of the Cells of the primary 

 row by cell-division, in correspondence with the general increase in 

 the size of the Anther ; until at length they form masses of con- 

 siderable size, composed of large squarish cells, filled with granular 

 contents, well-defined as constituting a distinct tissue from the 

 walls of the Pollen-Chambers. The history of the development of 

 the Pollen-Grains in their interior is thus described by Mr. Henfrey, 



* See Mr. R. H. Solly's description and figure of the petal of the Ana- 

 gallis, in "Trans, of Soc. of Arts," Vol. xlviii. 



