•360 A. B. RENDLE ON THE USE OF MICROSCOPICAL CHARACTERS. 



■of which we know little or nothing, and which might well form the 

 subject of a separate address. A certain form may be charac- 

 teristic of a family, as for instance the spiny pollen of the Mallows ; 

 or, on the other hand, a remarkable variety may occur in one and 

 the same family, as for instance in the Acanthaceae, where the 

 difierent genera show remarkably varied and characteristic pollen- 

 forms. 



In the family Convolvulaceae the character of the pollen affords 

 a ready means of distinguishing genera that are otherwise closely 

 similar in characters of foliage, flower and fruit. Thus the genus 

 Ipomoea, the convolvulus of the tropics, which includes the Morn- 

 ing Glory and the so-called " Convolvulus major " of gardens, has 

 spiny pollen resembling that of the Mallows, whereas in the genus 

 Convolvulus, which includes our common bindweed, the pollen is 

 smooth. The series of lantern slides which follows shows on the 

 one hand a striking resemblance between the pollen of genera of 

 the same family, and on the other hand that there is often a remark- 

 able difference between the pollen-grains of allied genera ; the case 

 of the cornflower in the Compositae is an interesting illustration 

 of the latter. 



In conclusion, it is obvious that the systematist may derive 

 great help from the study of minute characters, but it is equally 

 obvious that single characters must be used with caution, and this 

 warning applies not merely to those which can be elucidated only 

 by use of the microscope. 



I should add that a large proportion of the lantern slides by 

 which I have been able to illustrate my address have been lent 

 me by my friend Dr. Rodman, our fellow-member, whose skill and 

 zeal in photomicrographic matters is well known to you. 



Jorirn. Quekctt Microscopical Cltib, Ser. 2, Vol. ZIIl., No. 82, Aprii 191^. 



