396 STRUCTURE OF PHANEROGAMIC PLANTS. 



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

 boiling "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. 1 



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 afford 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- 



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

 of Society of Arts," vol. xlviii. 



