396 STRUCTURE OF PHANEROGAMIC PLANTS. 



spirit-lamp, after which it is to he covered with a thin glass. The 

 hoiling "blisters" it, but does not remove the color; 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), together with many others of a small and delicate cha- 

 racter, are also very beautiful microscopic objects ; and the two 

 just named are peculiarly favorable 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 pre- 

 decessor ; 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 " splic- 

 ing on" of two new vessels diverging from one another, to the 

 end of that which formed the principal vein.' 



252. 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 aflbrd a good 

 opportunity of studying that "free" cell-development, which 

 seems peculiar to the parts concerned in the Reproductive pro- 

 cess, 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 ordi- 

 nary methods of multiplication (§§ 150, 198). 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, 

 consisting 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 

 considerable 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 de- 

 velopment of the pollen-grains in their interior is thus described 

 by Mr. Henfrey, who has made a special study of it. " The con- 



' See Mr. R. H. Solly's description and figure of the petal of the Anagallis, in " Trans, 

 of Society of Arts," vol. xlviii. 



