HYBRIDISING AND RAISING ORCHID SEEDLINGS. xxxv. 



incapable of being fertilised. An example will make this point clear. If 

 the ovary of an ordinary flower — a lily for example — be examined as soon as 

 the flower opens, the ovules will be found in a developed condition, so that 

 when the pollen is applied to the stigma the pollen tubes grow rapidly, 

 making their way down the tissue of the style, and into the ovary, when 

 they enter the micropyle (or mouth) of the ovule, and unite with the contents 

 of the egg-cell, this latter constituting the act of fertilisation, after which 

 union the ovule develops into a perfect seed. But if an Orchid flower be 

 examined at this stage the ovarian cavity and ovules will be found quite 

 rudimentary, and if the flower is not pollinated they will progress no further, 

 the flower at length shrivelling and falling off. But when pollinated a rapid 

 change takes place. The column and ovary begin to swell and the segments 

 to fade or change colour. The ovary often looks like a simple pedicel when 

 the flower expands, but after pollination it gradually takes on a capsule-like 

 appearance. The act of pollination applies a stimulus to the ovary, causing 

 it to swell, and the ovules to develop, after which only can fertilisation take 

 place. This retarded development of the ovary is one of the points in which 

 Orchids differ so markedly from most other plants, and is, of course, 

 correlated with the slow development of the pollen tubes. 



Cattleya Mossi.e. — In the case of Cattleya Mossise the whole process 

 has been worked out by Mr. Harry J. Veitch, who, by a series of experi- 

 ments, ascertained the fact that fertilisation does not take place until a 

 period of from 75 to go days after pollination. The process is briefly as 

 follows: A few hours after pollination the floral segments become flaccid, 

 and show signs of withering. In a couple of days the pollinia are seen to be 

 disintegrating, forming, with the viscid secretion from the stigma, a 

 gelatinous mass that quite fills up the stigmatic cavity. At the same time 

 the pollen tubes have commenced to grow, and in eight days they have 

 reached the base of the column, being found in vast numbers among the 

 conducting tissues. At the end of a month the ovary has become consider- 

 ably enlarged, and the placentae and ovules are beginning to assume a 

 definite form, while the pollen tubes are pushing downwards along the sides 

 of the placentae and among the ovules. In two months, though the pollen 

 tubes are present in countless numbers, and have even reached the base of 

 the ovary, the ovules are not yet developed, but soon afterwards they rapidly 

 undergo a change of form, and at the end of about three months the long 

 looked-for event takes place. The pollen tubes now enter the micropyle of 

 the ovule, and fertilisation of the egg-cell is effected. It is noteworthy that 

 before this event takes place the ovary has developed from a terete body, 

 less than a quarter of an inch in diameter, to a six-angled one, more than 

 seven times as broad, entirely through the stimulus given by the act of 

 pollination, and it enables one to realise to some extent why a seed pod may 



