30 ROOT HABITS OF DESERT PLANTS. 



WINTER ANNUALS. 



Between the months of November and March, and occasionally one month 

 before and one month after that period, if the moisture conditions are 

 favorable, a large number of annuals make their appearance in the different 

 habitats considered in this study. These are for the most part of different 

 genera and species from those which occur in summer, and like the latter 

 have to a large degree a generalized type of distribution. Often the same 

 species of Avinter annuals are to be found wherever the soil and the water 

 conditions are suitable irrespective of the habitat, whether Tumamoc Hill 

 or the lower-lying bajada, but they may be present in greatest profusion on 

 the lower slopes of the Hill. The following winter annuals were examined : 



Amsinckia spectabilis Fischer and Meyer. Hordeum murinum L. 



Astragalus nuttallianus DC. Malva borealis Wallm. 



Bowlesia lobata R. and P. Malacothrix clevelandi Gray. 



Brodia'a capitata Benth. Medicago denticulata Willd. 



Daucus pusillus Michx. Mentzelia albicaulis Dougl. 



Eritrichium pterocaryum Torr. Microseris linearifolia Gray. 



Erodium cicutarium (L.) L'Her. Monolepis chenopodioides Moq. 



Festuca octoflora Walt. Orthocarpus purpurascens Benth. 

 Gilia bigelowii Gray. var. palmeri Gray. 



Harpagonella palmeri Gray. Parietaria debilis Forst. 



Amsinckia Spectabilis. 



.4 msinckia spectabilis is one of the most abundant of the winter annuals 

 and, as far as its local distribution is concerned, one of the most generally 

 distributed. It also is one of the most drought-resistant, a condition 

 which is illustrated by the following note on its behavior. In the spring of 

 1907 one of the staff of the Desert Laboratory was studying the invasion of 

 plants into a denuded area. On March 19 the storms of winter were over 

 and the arid conditions w^ere rapidly becoming marked ; on that date the 

 temperature out-of-doors in the shade was 94° F. with a relative humidity 

 of 20 per cent. The winter annuals were for the most part already dead. 

 On the periphery of the denuded plot mentioned there had been a heavy 

 growth of Sisymbrium reflexum, Bowlesia lobata, Amsinckia spectabilis, and 

 Phacelia tanacetifolia. Of these annuals the first two were nearly all dead 

 and were shedding their seed, while the last two were apparently unaffected 

 by the drought, though all of these plants were apparently under similar 

 conditions. 



Amsinckia has a deeply penetrating main root and numerous laterals, 

 all of which, especially in the young plants, are slender and branch but 

 little. The root-system is extensive rather than intensive.* As the plant 

 becomes older the tap root becomes heavier, and the difference in diameter 

 between it and the laterals is somewhat accentuated. 



As in the summer annuals, the length of the main root as given in this 

 paper is usually somewhat less than the actual length, owing to the diffi- 



*Where roots are thus characterized it is not intended to classify them after Biisgen, 

 unless so stated, but the words are merely used in a descriptive sense. 



