248 Variation in Wild Hop 



(3) Relative Number of Glands on the Leaves. 



The under surface of the leaves bears yellow glands easily visible 

 with a lens. It was found that the glands were more densely crowded 

 on some plants than on others. In order to ascertain whether this 

 character was of systematic value an estimate of the relative number of 

 glands present on the leaves was necessary. For comparative results it 

 was considered sufficient to record the number of glands found on a 

 certain portion of each leaf examined, the area and situation of that 

 portion being the same for all leaves. Countings were therefore made 

 of the number of glands within a \ inch circle on that part of the leaf 

 midway between the base of the lamina and one of the two sinuses at 

 the base of the terminal lobe of the leaf; two countings were thus pos- 

 sible on each leaf, one on each side of the midribs The countings were 

 taken during from two to five seasons, several leaves being taken for 

 each plant each year. The leaves were taken about half-way between 

 the lower wire and the top wire, the examination being made as the 

 plants came into flower. 



Although there was considerable fluctuation in the number of glands 

 occurring on leaves of the same plant taken in successive years and even 

 on leaves taken from the same bine, nevertheless evidence was soon 

 obtained that the leaves of some plants were more glandular than those 

 of others. In 1916 and 1917 four or eight countings were made each 

 year, according to the number of suitable leaves present on the plant at 

 the time the examination was made; in subsequent years (1918-20) the 

 greater number of plants which came under observation did not allow of 

 so many actual countings but a sufficient number of leaves was examined 

 to enable a general average or range of fluctuation to be estimated. 



It was found that in some plants the number was invariably below 

 the average, in others invariably much higher, while there were many 

 transitional forms between the extremes. Examples are given in the 

 following table, the figures, as explained above, showing the number of 

 glands in a ^ inch circle. 



It will be observed that, of the three plants to which references have 

 been made previously as being " very early " and having " green " bines, 

 two, viz. Z 17 and Z 42, are included among those plants in which the 

 leaf glands may be described as " many"; actual countings in the case 



1 For rapidity and convenience a thin piece of sheet metal, perforated at the centre 

 with a circular hole \ inch in diameter, was placed on the leaf in the place indicated, and 

 by means of a lens all the glands seen within the circle were counted. 



