Mainz, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Mainz, Univ., Diss., 2001. / Computerdatei im Fernzugriff.

Mainz, Univ., Diss., 2002. / Computerdatei im Fernzugriff.

Mainz, Univ., Diss., 2002. / Computerdatei im Fernzugriff.

Mainz, Universiẗat, Diss., 2001.

Mainz, Universiẗat, Diss., 2002.

Universiẗat, Diss., 2002--Mainz.

The mistletoe Phoradendron californicum is a common parasite on the mesquite plant Prosopis juliflora. Seeds of the parasite are deposited upon the host plant by birds and perhaps other agents. Normally seedlings of the parasite become established when the elongating radicle of the embryo comes into contact with a host branch and forms a holdfast. From the underside of the holdfast the primary haustorium enters the host tissue and establishes the parasitic union. Later the aerial portion of the parasite develops. Some seeds of P. californicum follow a different sequence; they stimulate the host to produce gum in the tissue beneath the seed by apparent dissolution of cells. The exuded gum elevates the developing seed from the host branch preventing establishment of the host-parasite union. The possible significance of this apparent defense mechanism is discussed.

Discoveries revolving around false hellebore (Veratrum californicum Durand) have caused a paradigm shift in treatment from eradication to harvest and preservation. Test plots set in place 18 years ago to analyze the effectiveness of eradication treatments (tilling, herbicide, mow, and remow) give us a better idea of how false hellebore communities might respond to disturbances caused by harvest. We focused mainly on the tilling, mow, and remow treatments because of similarities to harvest techniques.We found that mow and remow treatments have little effect on the population of false hellebore in the wild. Tilling treatments were effective in reducing the population dramatically; however some recovery in numbers has taken place. Tilled plots showed a significant decrease in mid seral plant populations, and a significant increase in early seral populations. Tilled treatments were also opened up to intermediately desirable and undesirable plants. Mow and remow treatments reacted similarly to each other, with mow treatments showing decreases in mid seral species and with both treatments showing neither an increase nor a decrease in the other seral stages. Mow and remow plots showed a decrease in desirable plants, but an increase in intermediately desirable plants and no increase in undesirable plants. Greenhouse experiments were unsuccessful due to phenological disruptions caused by removal from the native habitat as well as climate and temperature differences.

No description available.