526 T. Holm — Ceanothus Americanus and ovatus. 



portion of the primary root has become compressed, and very 

 prominently so at the base. By examining the internal struc- 

 ture we readily noticed that a very irregular growth had taken 

 place. The rays of hadrome had increased in thickness much 

 more on the one side of the root than on the other, thus the 

 vessels showed the arrangement somewhat similar to a fan. 

 A similar case has been reported by Wigand,* who observed 

 that while the primary root in Ononis repens and sjpinosa 

 shows a normal and concentric growth during the first year (at 

 the seedling stage), it exhibits a very conspicuous, excentric 

 increase in the succeeding year. This is due to' the one-sided 

 enlargement of the hadrome ; besides that the medullary rays 

 have not only been prolonged, but also very considerably 

 broadened towards the periphery in exactly the same way as 

 in our Ceanothus. The so-called " Bretterwurzel " described 

 by Haberlandtf shows the same structure, but this root-type 

 has a special function which cannot be attributed to the roots 

 of either Ononis or Ceanothus, since these are completely 

 underground. It is an anomaly, which seems to be rare 

 among shrubs and herbs, and we are unable to offer any expla- 

 nation as to its cause ; we can only state that all the specimens 

 examined of C. Americanus and ovatus showed this root- 

 structure when more than a year old, and that it seems very 

 improbable that it might be due to the nature of the soil, 

 since the one of these species (C. Americanus) grows in clay- 

 ish or somewhat sandy soil, while the other seems to thrive 

 only among rocks with the roots tightly pressed in the narrow 

 fissures. It would be interesting to know whether the numer- 

 ous Californian species behave in the same manner. 



If we examine a plant in the third season (fig. 4), we notice 

 the same principal structure as shown in our figure 3. The 

 hypocotyl (H) is still very distinct, and the scars from the 

 cotyledons (Cot.) are plainly visible with two stem-bases from 

 the preceding year (St.), while there is no trace of the primary 

 stem above the cotyledons. Young lateral shoots develop now 

 from the basal leaves of the stems of the previous year ; they 

 are yet purely vegetative and die oif to near the base during 

 the fall. In regard to the root, this has increased very con- 

 siderably in length and thickness ; the irregular structure is 

 very pronounced, and the mycorhizse are quite large, but do 

 not yet show any signs of ramifying. 



When the plant has reached the age of about five years it 

 commences to flower ; the ramification, however, is exactly the 

 same as described above, and the flowers develop exclusively 

 upon shoots of the same season. One point deserves men- 



*Einige Beispiele anomaler Bildung des Holzkorpers. (Flora, 1856, p. 

 674.) 



f Eine botanische Tropenreise. Leipzig, 1893, p. 104. 



