ltOYAL HORTICULTURAL SOCIETY. 



grains in their pollen. The pollen of all other European willows is 

 remarkable for its great regularity. One grain is almost perfectly- 

 like another in size, colour, constitution, and form ; and pure 

 species are peculiarly distinguished by this character from hybrids, 

 in whose pollen, amongst a greater or less number of large, regular 

 grains, there are always some which are abnormal. Moreover the 

 various hybrids differ greatly from each other in this respect. 



Hybrids whose pollen contains no perfectly developed grains, 

 and hybrids which amongst normal pollen-grains contain only a 

 small percentage of irregular grains, stand at the two extremities 

 of a series which numbers almost as many intermediate links as 

 there are hybrids. It may be asked of what nature is the irregu- 

 larity of hybrid pollen ? How do the differently formed grains 

 comport themselves with respect to potency ? How are they 

 developed ? In what relation do the different degrees of irregu- 

 larity which we recognize in hybrids stand to their composition ? 



These irregularities are of six kinds. 



1. Linear elongated bodies, about the size of an anther-cell, 

 which contain within a membrane a large number of dark, dirty- 

 yellow, round pollen-grains of somewhat more than the usual size. 



2. Irregular bodies, consisting of from two to four full-grown 

 grains, sometimes light, sometimes of a dark dirty yellow, which 

 contain a great mass of oil. 



3. Grains nearly twice the usual size, of a dark dirty yellow, 

 scarcely transparent, otherwise of the regular orbicular form, and 

 containing much oil. 



4. Globular bodies, three, four, or ten times smaller than the 

 normal grains, colourless and almost translucent. 



5. Grains which differ only in a small increase or diminution of 

 size from normal grains, with which, moreover, they agree in the 

 pale colour, semitransparent aspect, and in the regular develop- 

 ment into a ball when placed in watery fluids. 



6. More or less regularly plicate, dark, impellucid bodies, of the 

 normal size or smaller, which, placed in water, are unaltered and 

 do not assume a spherical form. 



The last form is the most common, and exists in pure S.fragilis 

 and triandra ; 4 and 5 often occur together. No. 3 is uncommon, 

 and 1 and 2 very rare. No. 1 has occurred only in a spontaneous 

 hybrid between IS. cinerea and incana, and No. 2 only in a very 

 few instances. 



Imperfections in the sexual organs of hybrids have, however, 

 been shown by Gsortner and others to go further in other plants 



