THE POLLEN-GRAINS 343 



Pollen-grains as a Possible Aid in the Study of Hybrids. I am 

 greatly indebted to my friend Mr. J. S. Slater for having devoted 

 much time and attention to the study of the pollen-grains of this 

 genus. Mr. Slater informs me that he commenced the study of 

 pollen-grains with a view to ascertain whether any light could 

 thereby be thrown on the origin of hybrids. A selection of the Source of 

 more characteristic species of Gossypium, each drawn from two or grams- 

 three independent and often remote localities, having been furnished 

 by me, the pollen-grains of these (taken from flower-buds as far as 

 found possible, in order to avoid contamination), were carefully mounted 

 in the form of microscopic slides and then critically and comparatively 

 examined. The grains shown on each slide were derived from but 

 one anther, or at all events from the selfsame andrcecium. Every 

 precaution was thus observed to ensure accuracy, not an easy matter 

 when working with dried herbarium specimens that have often to be 

 boiled before they can be examined at all. The method of examination Method of 

 pursued may be said to have been as follows : When buds were t^ 11 

 obtainable they were boiled in water so as to facilitate the removal of 

 the pollen -grains. When flowers only were available a few anthers 

 were removed, and from these the grains were derived by cutting open 

 in a drop of 10 per cent, solution of chloral hydrate. The moisture 

 was thereafter removed by absorption. The grains were then stained 

 in ' Bismarck-braun ' and finally cleared in absolute alcohol and 

 mounted in Canada balsam and xylol. Uniformity in treatment 

 having been thus observed, the results may be regarded as relatively 

 correct. In Mr. Slater's opinion boiling or non-boiling does not 

 affect the shape or size of cotton pollen-grains. 



Mr. Slater was good enough to place in my hands an extensive 

 series of these microscopic slides, as also to furnish micro-photo- 

 graphs, some magnified 450 and others 300 times life-size. I have 

 had reproduced a few of these photographs, on Plates Nos. 52 and 53, Micro- 

 but the selection has been governed by the desire to exemplify the graphs, 

 more striking peculiarities observed, rather than to expound any 

 theories that might be advanced regarding their structural pecu- 

 liarities. The results of this special and comparative study of the 

 pollen-grains of a large percentage of the species, varieties and races 

 of Gossypium, so far as it has gone, would seem, however, sufficiently 

 suggestive to warrant the main ideas being here indicated, even 

 although it would be premature to lay down definite conclusions. 

 The remarks that follow must accordingly be accepted as purely 



