164 SEVENTH REPORT. 



WINTER FIELD WORK IN BOTANY. 



J. HARLEN BRETZ. 



Under winter conditions, perennial plants face a very different prob- 

 lem than in summer. With the oncoming of winder, marked changes in 

 the environmental conditions take place, of which the most pronounced 

 occur in the factors of temperature and water supply. Low temperature 

 indirectly and lack of water very directly force the plant into suspension 

 of activity. Endurance becomes the test of fitness to survive. 



To meet these changes, the plant becomes xerophytic, taking many precautions to pre- 

 vent escape of water by evaporation since it can secure none to replace any loss. It 

 might be said that plants of temperate and colder regions become pseudo-xeroph\'tes in 

 winter. Xerophxtes, they of course are not because the true xerophyte works under its 

 conditions. 



One response to the changed conditions is the formation of winter buds and in these 

 the endeavor of the plant to preA'ent evaporation is clearly sho'WTi. It is on these buds 

 that a great deal of the work of plant identification must be done. 



A few instances will show that this work is not so difficult as at first it might appear. 

 The four species of Hicoria most commonly found present no difficulty in identification 

 from winter buds. Hicoria ovata, the shagbark hickory, has a large, oval, yellowish 

 brown bud with two dark outer scales that shag off, Hicoria alba lacks the outer scales, 

 Hicoria glabra has a smaller bud than H. alba though similar otherwise and Hicoria min- 

 ima, the swamp hickory, has a long, flattened, winter bud of a bright orange yellow. Again 

 it would be difficult to distinguish between the two species. Viburnum I.entago and Vi- 

 burnum prunifolium, in winter were it not for this mark of identification. The buds of 

 V. Lentago are long and acute while those of V. prunifolium are shorter and thicker and 

 are often covered with a rusty pubescence. It may be necessary occasionally to secure 

 both species for comparison before one can be definitely certain. Another example may 

 be found in the genus Fraxinus. The only two species commonly found in southern 

 Michigan, Fraxinus Americana and F. nigra, are distinguishable at a glance for the buds 

 of F. nigra are a dark brown, almost a black, and could hardly be mistaken for those of 

 Fraxinus Americana, the white ash. 



If there is not sufficient differentiation in the bud, it is a simple matter to carry a twig 

 home and force the bud into expansion. A beaker of water and a south window will 

 bring it out and often enough additional data will be afforded by the leaf which will par- 

 tially develop, to decide the species. 



We, of course, can not deal with annuals in this use of winter buds. But, except for 

 this restriction, the annual is not barred from the scope of winter work in identification. 

 Nearly every annual plant whose bare skeleton stands through the winter has some with- 

 ered, wrinkled leaf still clinging to it. More often it will be found near the base of the 

 plant, perhaps covered by the snow. Steaming or a brief immersion in water will unfold 

 the contorted leaf and admit the determination of its shape, marginal and base form, 

 venation, attachment to stem, whether sessile or with a long petiole and many other 

 marks which may characterize a species. 



Melilotus officinalis and Melilotus alba, the common sweet clovers of every roadside, 

 are not to be distinguished in winter without examination of the leaflet. That of M. 

 officinalis is narrowed at the base, that of M. alba is oblong. 



Suppose all the leaves have been lost, yet their arrangement on the stem is still to be 

 easily observed, from the leaf scars. 



Still more data are afforded by a study of the culm of the annual. Is it terete, quad- 

 rangular, triangular, flattened, grooved or ridged? Hollow or solid? Glabrous or pu- 

 bescent? 



The stem or twig of woody plants gives a like latitude for specific variations. Hicoria 

 minima can be distinguished across a field, with no examination whatever of its bud. 

 Its slender, graceful twigs and branches are almost feminine beside the angular, roughened, 

 thicker branches of the other hickories. 



Modifications of the epidermis are more common. The vivid red bark of the osier, 

 Cornus stoionifera, is easily distinguished against the snow from the kinnikinnic osier, 



