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ROYAL HORTICULTURAL SOCIETY. 



prevent the separation of the mother- cells. In mature anthers 

 these confluent pollen-grains form yellow linear bodies ; when 

 pressed out of the immature anther they have an appearance like 

 that of frog-spawn. 



The four next forms arise from an irregular division of the 

 mother cells. In hybrids in which these forms occur, sometimes 

 we find the mothercells only uniseptate, and in consequence two 

 large pollen-grains are formed instead of four half the size. Some- 

 times, though the cells are quadriseptate, the division is irregular, 

 and one larger grain with three smaller ones is often the conse- 

 quence. A further cause of irregularity arises from the fact that 

 the dissepiments of the mother cells are so imperfect that the 

 pollen-grains of the different component sacs are confluent with 

 each other. In this way the compound grains of No. 2 arise, 

 consisting of two or more confluent individuals. More rarely the 

 cells divide into a larger number, from sixteen to twenty, and the 

 grains are consequently minute. In "No. 6 the division of the 

 mother-cell is at first apparently normal, as are also the pollen- 

 grains, and the malformation first appears when the pollen-grains 

 begin to contract. The triple folding does not take place. One 

 half of the globe remains convex, the other is pushed in, so that a 

 purse-like body is formed, or, if the triple folding takes place, it 

 is very irregular. In either case, the dark colour and want of 

 transparency show that the fluid contents of the grains are more 

 or less deficient. 



It is worthy of remark that the irregular division of the mother- 

 cells does not necessarily induce sterility. On the contrary, the 

 pollen-grains of a greater size than usual, which arise from the 

 irregular division of the mother cell, are frequently fertile. Steri- 

 lity attaches rather to those recklings which are below the normal 

 size and which are generally colourless and transparent, to those 

 which are not expanded when in contact with fluids, or, finally, to 

 those which are extravagantly large and confluent, if of a dark 

 brownish yellow. This change of colour depends probably upon 

 some anomalous composition of the fluid contents. 



It is scarcely possible to classify hybrids according to this im- 

 perfection of the pollen, because the gradations are so gentle; 

 certain laws, however, seem to prevail. 



1. The anomaly of the pollen increases with the succession of 

 generations arising from the fertilizing of hybrids with their own 

 pollen. This is the case with hybrid willows ; and Grs&rtner has 

 shown that, with respect to hybrids of Aquilegia, Dimthus, Lava- 



