THE GENUS GOSSYPIUM 57 



that occasionally the pigment is little if at all developed, while in 

 others it is so pronounced as to originate the description 'nigro- 

 punctate.' In some few species these intercellular glands protrude 

 on the surface of the petioles and peduncles so conspicuously as to 

 almost assume the condition of warts or tubercles and to give a rough 

 or spinose appearance. They are usually more apparent on the 

 petals and capsules than elsewhere, and in the latter case very often 

 rise above the surface. If the fresh petal be placed between clean 

 paper and pressed firmly, the gland-dots will be seen to impart a 

 yellow stain with a purple central spot. Miers (MS. notes) has 

 pointed out that the purple spot is soluble in water, and the yellow 

 stain in alcohol. According to some writers, the presence of the 

 gland-dots on the cotyledons, has -been accepted as generic. 

 (Lubbock, ' Seedlings,' i., 1892, pp. 259-60.) These are apparently 

 universally present in Gossypium, but are not fully formed. They 

 appear as minute elevations on the surface, but do not sink within 

 the tissue, nor become coloured in the way characteristic of the 

 normal leaves. Lastly, the prevalence of gland-dots in the leaves 

 is more constant with Gossypiiim than with the allied genera, where 

 they are often restricted to the flowers and fruits. 



2. Glands on the veins of the leaves. The early botanists Foliar 



11 



placed considerable importance on the presence of glands on the 8 

 midribs (seen on the under-surface) of the leaves of Gossypla. 

 Certain species were in fact regarded as distinguished by the 

 absence of such glands, others by the presence of only one gland 

 on the middle vein, while others possessed three or more. There 

 would seem little doubt that a tendency is manifested on the part of 

 the non-cultivated species to preserve a fixed condition in these 

 respects, but that with the cultivated forms variability might be said 

 to become the rule, a consequence either of direct adaptation to 

 environment or a consequence of hybridisation. While, therefore, 

 the presence of glands need not be accepted as diagnostic, they 

 are nevertheless often of value in distinguishing species, their 

 absence being occasionally a more valuable characteristic than their 

 presence. These midrib glands may be elongated and elevated 

 portions of the vein that become pale-coloured or assume a pink 

 tinge, and then rupture lengthwise ; or they may be circular or 

 oblong warts which open into distinct pits. In either case they 

 discharge a minute drop of nectar, eagerly sought after by sugar- 

 loving insects. 



