GENERAL CONCLUSIONS AND SUMMARY OF STUDIES ON 



ANNUALS. 



On Tuiiiamoc Hill, and that portion of the bajada and the ll<jud-plain of 

 the Santa Cruz river within the Laboratorj' domain, as well as by the West 

 Wash, 22,'? species of annuals are reported. Of these, 1 22 are winter annuals 

 and 44 appear in summer. Representative species both of winter annuals 

 and of simimer annuals, as well as one or two perennials and long-lived 

 annuals, were examined in connection with the present study. In looking 

 over the results of observations on root-systems, several facts were brought 

 to light, of which the following appear at present to be the most important. 



A feature of several species of both winter and summer annuals is the 

 presence of rudimentary roots in certain species and their consistent absence 

 in others. Among the plants with rudimentary roots are Amsinckia, Eritri- 

 chinm, Hai pagonella, Peciocarya, Erodium, and Malva, among the winter 

 annuals, and Amaiantlius, Boerhaavia, Cladotlnix. and Trianlhciiia among 

 those of summer. Frequently associated with the presence of the root 

 rudiments, perhaps always so, is the appearance of laterals, particularlv 

 those of the first order, in groups of three or four; another feature is the pre- 

 cocity of rudimentary-root formation in several species, particularly in 

 A»!sin<:kia and its relatives. With the desire to throw some light on the 

 causes underlying the appearance of the rudiments the following experi- 

 ments, which are regarded as preliminar>', were set up. 



On February 14 two pots were planted with seeds of Amsinckia spedabilis. 

 At the time of the sowing of the seeds the pots were thoroughh- watered, 

 after which one was not given water again and the other was watered 

 frequentlv. About April 6 the young plants in the dry pot were seen to 

 be in a wilting condition and were removed from the pot and their roots 

 examined. It was found that the laterals of the first order were borne 

 singly on the main root and that at the base of each lateral there were one 

 or two rudiments. The rudiments of the smallest plants in the pot were 

 best developed. The root-systems of the plants growing in the well- watered 

 pot had the following characters : the laterals of the first order were mostlv 

 in pairs, and at the base of each group there was at least one rudimentary 

 root. It would appear, therefore, that the organization of the rudiments 

 in .4 nisinckia is not dependent on an improvement of the water conditions, 

 although their subsequent development is. and that they are to be con- 

 sidered a constant character in the root-system of the species. 



In many of the plants no rudiments were seen at any time ; experiments 

 were set up, consequently, to learn whether the formation of rudimentarv 

 roots might be induced; the experiments were confined to Rafinesquia neo- 

 mexicana and the conclusions are not assumed to be applicable to any 

 other species. In December a pot of suitable earth was prepared and was 

 thoroughlv soaked with water, and seeds of Rafinesquia were sown. After 



40 



