REPRODUCTION— THE FLOWER. 



55 



in Passion-flowers and some other plants fer- 

 tilization cannot be effected by a flower's own 

 pollen even when carefully deposited by the 

 experimenter. The flower indeed in such cases 

 refuses to be fertilized by its own pollen, and 

 requires the application of that of some other 

 nearly allied species. But, on the one hand, 

 close-fertilization may sometimes occur, and on 

 the other hand an occasional cross may be effected 

 in flowers that are habitually close-fertilized. On 

 the whole, cross - fertilization is advantageous, 

 and secures a larger proportion of continuously 

 healthy seedlings than does close -fertilization, 

 or "in-and-in breeding". 



Artificial fertilization is sometimes practised 

 in gardens, when the pollen is removed with a 

 camel's-hair brush and applied to the stigma of 

 the same or some other flower of the same 



species. 



Hybridization. 



This differs from cross-fertilization only in 

 degree. Cross-fertilization occurs between two 

 separate flowers of the same individual plant, or 

 between flowers of different individual plants of 

 the same species. Hybridization is the fertili- 

 zation of the flower of one species by the pollen 

 of the flower of another species. Generally 

 speaking the two species must be nearly allied, 

 the more nearly so the more likely is the cross 

 to be effected, the wider the difference the less 

 likely is the cross to be successful. No doubt 

 hybridization does occur in nature, but it is not 

 common. A proof that it does occur is offered 

 by some Orchids and Narcissus. These par- 

 ticular forms when first introduced were sup- 

 posed to be hybrids from their combining the 

 characteristics of two species. When the two 

 parent species were known to grow in the same 

 locality the inference was strengthened. But 

 the case has now been demonstrated in gardens 

 by the hybridizer actually producing the same 

 form by fertilizing artificially the one flower by 

 the pollen of the other. 



To effect hybridization great care is necessary 

 to prevent the pollen of the flower to be hybri- 

 dized from gaining access to its own stigma; 

 hence hybridizers are careful to remove the 

 stamens of the flower they are operating on, 

 and to cover up the flower with muslin after 

 the operation, so as to prevent the entry of 

 insects. 



When it is desired to keep any particular 

 "stock" true, it is desirable — in some cases 

 imperative — to grow no other plants of the same 

 nature in the vicinity. The flowers of the 



cabbage genus (Brassica) are specially liable to 

 intercross in this way if care be not taken to 

 keep the stock true in the manner indicated. 

 Cross-breeding and hybridization form most 

 valuable means to the gardener for the produc- 

 tion of new forms; but inasmuch as it often 

 happens that the cross or the hybrid is not so 

 good as either of its parents, it is specially 

 desirable that the crossing should not be done 

 hap-hazard, but that the cross-breeder should 

 formulate in his own mind, before operating, 

 what results he wishes to obtain, and then 

 select those plants for crossing which are the 

 most likely to ensure the results he desires. A 

 vast number of mongrel seedlings which are 

 now raised are practically worthless, and entail 

 disappointment and loss of time to the raiser. 

 These evils might largely, if not entirely, be obvi- 

 ated by a more systematic course of procedure. 

 In any case accurate records should be kept, and 

 every care taken to ensure success. Nor should 

 the hybridizer be discouraged by want of success 

 in the first instance. A first cross often results 

 in the appearance of a number of unattractive 

 or useless forms, but by continuing the process 

 of crossing, and selecting for breeding purposes 

 only the best and most suitable, the desired 

 results may in many cases be secured. (See also 

 chap, ix.) 



Sports. — The appearances presented by cross- 

 breds and hybrids are very often difficult to be 

 accounted for. Still more mysterious is the 

 sudden appearance of sports or bud-variations. 

 These latter may in some cases be accounted for 

 by the separation of the heretofore mixed char- 

 acteristics. The changes that occur in the nuclei 

 in the course of their subdivision may also even- 

 tually furnish an explanation. These changes 

 are very complex and obscure, so that they can 

 only be briefly alluded to. It must suffice to 

 say that the nucleus consists of a number of 

 curved threads closely interwoven (fig. 68). 

 When the nucleus divides it not only does so 

 transversely, so that two groups of threads are 

 formed, but each thread divides lengthwise. In 

 the process of fertilization, as we have seen, two 

 nuclei coalesce into one; that one must neces- 

 sarily be formed of the threads belonging to its 

 two predecessors. When its turn comes to 

 divide, its threads divide, as we have seen. 

 Generally speaking the division is quite equal, 

 each subdivision containing an equal number of 

 threads. But it is quite conceivable that this 

 accurate distribution may sometimes not happen, 

 and then we should get divisions not of equal 

 nature, and from this primordial inequality what 



