SEED DIVISION. 49 



stamens are in different flowers. In cucnmbers, melons, and allof tbat 

 family, they are in different flowers on the same plant. Sometimes the 

 two kinds of flowers are borne by separate plants, as in the beet. In a 

 perfect flower the usual arrangement is for the pistils to occupy the 

 center, and to be surrounded by the stamens. The parts m.osfc iuti- 

 inatoly concerned in the production of a seed are the ovule and the pol- 

 len, the one to be fertilized and the other the fertilizing agent. 



"Crossing or hybridizing," says Thomas Meehan, editor of the Gar- 

 dener's Monthly, "is a very simple process. We take the pollen dnst 

 from one flower and place it on the apex of the pistil of another. To 

 make sure that the flower you wish to raise the seed from does not get 

 its own pollen, it is best to open the flower before it naturally expands 

 and cut off its antlers before they have a chance to throw out their pol- 

 len. At the same time it Is best to put the pollen of the male parent 

 at once on the stigma. The stigma is usually not receptive, that is, has 

 not the liquid exudation necessary for tlie eflective reception of the 

 pollen at this early stage, but it remains on the stigma ready for use 

 when the stigma is ready to receive it. These precautions are neces- 

 sary in order that we may be sure the flower receives only the pollen 

 we desire it to receive. Some cover the flower after the antlers have 

 been removed, until the time for the use of the pollen has arrived, with 

 gauze to keep off insects that might bring other pollen, but this is 

 scarcely necessary when done in the way suggested." 



POLLEN. 



" Pollen," says Gray, who is the highest authority in botanical matters, 

 "is the product of the anther, and is usually a powdery substance which, 

 wlien magnified, is seen to consist of separate grains of definite size and 

 shape, uniform in the same plant, but often very different in diflerent 

 species or families. The grains are commonly single cells, globular or 

 oval in shape, and of a yellow color. Pollen grains are usually formed 

 in fours, by the division of the living contents of mother-cells first into 

 two, and these again into two parts, which become specialized cells. 

 As the pollen completes its growth the walls of the mother-cells are 

 usually obliterated. A pollen has two coats. The outer coat is com- 

 paratively thick, and often granular or fleshy. This is later formed 

 than the inner, and by a kind of secretion from if; to it all the marlc- 

 ings belong. The inner coat, which is the proper cell wall, is a very 

 thin, delicate, transparent, and colorless membrane of considerable 

 strength for its thickness. 



. " The cavity inclosed by the coats is filled with a viscid substance, 

 which often appears slightly turbid under the higher powers of ordinary 

 microscopes, and, when submitted to a magnifying jDower of about 30:) 

 diameters, is found to contain a multitude of minute particles, the 

 larger of which are from one four-thousandth to one five-thousandth oi 

 an inch in length, and the smaller only one-fourth or one-sixth of this 

 :-ize. When wetted, the grains of pollen promptly imbibe water by en 

 Tiosmosis, and are distended, changing their shape somewhat, and ob- 

 literating the longitudinal folds, one or more in number, which many 

 grains exhibit in the dry state. Soon the more extensible and elastic 

 inner coat inclines to force its way througii the weaker jjarts of the 

 outer, especially at one or more thin points or pores, sometimes forming 

 projections when the absorbtion is slow and the exterior coating tough. 

 In many kinds of pollen the grains, when immersed in water, soon dis- 

 tend to bursting, discharging their contents. 

 4 AG— '85 



