60 



THE GARDENER'S ASSISTANT. 



are receptive, and are often fertilized by pollen 

 from other flowers long before their own anthers 

 are ready, or their pollen ripe. Then, in other 

 cases, flowers of two or three kinds, i.e. dimor- 

 phous or trimorphous, are borne by the same 

 plant, or even on the same inflorescence, as in 

 Primulas, which have long-styled and short- 

 styled flowers, or Lythrum, which has tri- 

 morphous flowers, or as in the case of some 

 orchids such as Catasetum, in which male and 

 female and hermaphrodite flowers are all oc- 

 casionally borne. In this way we see that even 

 hermaphrodital flowers often obtain the advan- 

 tages gained by those which are monoecious or 

 dioecious, and as a broad rule all such flowers 

 are more predisposed for cross-fertilization, and 

 so, as it were, lend themselves to the gardener's 

 or hybridizer's hand. 



After pollination, i.e. after the pollen-grains 

 have been applied to the stigma, it in a sense 

 begins to grow. A very slender thread-like tube 

 is protruded from each little pollen-grain, and 

 these tubes grow, i.e. they force themselves, or 

 are attracted down through the soft and spongy 



united characters of its two immediate parents, 

 and also hereditary traits derived from some at 

 least of its many former ancestors. In this way 



Fig. 74. -Longitudinal Section of a Pistil, with a Single Basal and Ana- 

 tropous Ovule, showing the course of the Pollen Tube. 



tissues of the style or pistil, so as to eventually 

 reach the ovules or young seeds (fig. 74). 



The growing point of the pollen-tube enters 

 the ovules by a little aperture called the micro- 

 pyle, and in this way a union is effected between 

 the sperm matter of the pollen and the germ 

 matter of the young ovule (fig. 75). In other 

 words, the ovule becomes fertilized, and begins 

 its development as a seed containing a living 

 germ or embryo that contains within itself the 



Fig. 75.— Ovule after fertilization, s, Embryo-sac with developing endo- 

 sperm, e, Embryo. (After Prantl and Vines.) 



pollination may take place without fertiliza- 

 tion, but, on the other hand, it is impossible 

 for fertilization to occur unless pollination has 

 taken place. Of course it is necessary for pollen 

 to be fully developed or ripe, a fact generally 

 known by its escape from the slits or pores of 

 the anthers. On the other hand, the stigma or 

 the stigmatic surface to which the pollen is 

 applied must be what is called receptive, i.e. in 

 a fit state of development to receive it. 1 



There is, as a rule, no great difficulty about 

 the practical art of cross-fertilization or hybrid- 

 ism. The first thing is to decide exactly what 

 you desire to obtain as the progeny of any two 

 species of the same genus, or between any two 

 varieties of the same species, and then at the 

 right time you transfer the pollen of the one 

 parent to the stigmas of the other. This is 

 simply what the bees and the flies have done 

 for ages past, unconsciously no doubt, in their 

 search for wax and honey. But it is often de- 

 sirable, and sometimes absolutely necessary, that 

 the anthers of the female parent should be cut 

 out and removed before they shed their pollen, 

 so as to make sure that the stigmas are not fer- 

 tilized by the pollen of the same flower, for if 

 this should have taken place the application of 

 any other pollen will be useless or misleading. 

 This removal of the anthers of a seed-bearing 

 flower is called emasculation. 



The implements and appliances needed are 

 very few and simple. A good pocket lens and 

 a pair of small long-handled surgical scissors are 

 useful; so also is a needle thrust into a slender 

 handle, which is better than knife or scissors for 

 slitting up tubular flowers. A few neat little 



i The figs. 55, 56, 57, and 59, in the preceding chapters, should 

 be referred to in connection with the subjects of pollen, pollin- 

 ation, and fertilization. 





