92 THE AMERICAN BOTANIST. 



soon as the seed coats are ruptured so that plenty of water is 

 available, the seeds grow immediately. Some seeds of water 

 plants will not grow if kept moist, but if allowed to dry up 

 and then moistened will readily germinate. This is supposed 

 to be due to the cracking of the seed coats in drying which 

 thus allows the moisture to enter the seed. 



Orchid Seeds. — Most orchids produce immense numbers 

 of seeds, but the seeds themselves are usually very minute. 

 The embr}^o they contain are mere rudiments of a young plant 

 and as is well known, germinate and grow with difficulty. The 

 fact that so few plants result from a sowing of orchid seeds 

 has suggested the possibility that many of the seeds contain 

 no embryo and the immense number in a capsule give rise to 

 the suspicion that many of the ovules are never fertilized or 

 that possibly many of the seeds are produced parthenogenetic- 

 ally. A- writer in the November Botanical Gazette asserts that 

 in the examination of a large series of seeds from our native 

 Cypripediums none were found without embryos. When we 

 realize the immense numbers of pollen grains that are required 

 to ensure that all the seeds in a capsule will be fertile, the or- 

 chid's reason for bearing its pollen grains in connected masses- 

 so that they may be transferred in a body is apparent. 



Fertilizers and Crops. — For centuries man has known 

 that he cannot successfully grow crops of the same kind in 

 the same fields without heavy additions of fertilizer. The idea 

 was that the crops removed from the soil certain elements in 

 it, which had to be made good from the fertilizers. Since dif- 

 ferent crops take different substances from the field a "rota- 

 tion of crops" was established by which each field produced a 

 succession of different crops. Recent experiments, however, 

 go to show that in most soils there are food materials enough 

 for many crops of the same kind but that the reason plants 

 can not make use of them is that the roots of each crop leaves 



