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10.15 GOLF COURSE MANAGEMENT 73 of shoots is called a gametop te. Shoots can form from structures produced during sexual or asexual reproduction. During the sexual cycle, spores are produced that contain ge - netic information from both male and female parents. Under favorable conditions, the spore germinates, giving rise to a mass of chloro - plast-containing, threadlike green flaments called protonema, which can also be produced directly from shoots or bulbils. Protonema are capable of growing along the surface of almost any stable structure, but can easily desiccate if moisture is not available (10). This is perhaps the most vulnerable stage in silvery-thread moss's life cycle. As protonema develop, buds are produced that give rise to an individual s oot, which differentiates into stems and leaves. Silvery-thread moss produces an ex - tensive izoid system, enabling it to anchor to almost any substrate. The rhizoid resembles the roots of vascular plants, but silvery-thread moss rhizoids do not appear to have the ability to conduct water and nutrients internally (7). While silvery-thread moss is capable of both sexual and asexual reproduction (4), the most advantageous mode of reproduction in putting greens is not clear. For instance, during sexual reproduction, spores are released from fruiting bodies at the top of a stalk, similarly to the seeds of a dandelion. Because putting greens are typically mowed daily, it is likely the stalks containing the spores are removed or simply crushed by the weight of the mower; therefore, spore production is unlikely to be a viable mode of reproduction for established silvery-thread moss in a putting green. Spores may, however, play a role in the initial stages of invasion in a putting green that was previously uninhabited by silvery-thread moss. Once established, silvery-thread moss can spread from several asexual structures, which likely serve as the primary mechanisms for in - creasing the size of an infestation (12). For in- stance, regeneration can occur from fragmen- tation or through the production of specialized organs, such as bulbils (6). Fragmentation is a simple form of vegetative reproduction, and it occurs when a shoot is separated from the gametophyte (6). Fragments are capable of traveling long distances, but they are typically deposited in close proximity to the original ga - metophyte. Once deposited in a favorable site, protonema radiate from the fragment, produc - ing several hundred new shoots (6). Bulbils are small, highly condensed leaves and may be produced in large quantities from stems of silvery-thread moss (12,13). One to several can be produced per shoot (6). After they have been transported to a favorable site, bulbils "germinate" and produce new shoots or protonema. Shoot fragments and bulbils are buoyant and readily transported by water. A heavy rainfall or irrigation can therefore move veg - etative structures to previously uninhabited areas (10). Propagules (bulbils, shoot frag - ments and protonemal fragments) can also be transported from green to green by adhering to golfers' shoes or to maintenance equipment. Consequently, while sexual reproduction is likely important for long-distance dispersal of spores to previously uninhabited areas, re - Spores are produced inside the sporophyte, which is the small, headlike projection at the end of the stalk. This group of sporophytes was raised in a petri dish under laboratory conditions. Photos by Lloyd Stark Bulbils are small, highly condensed leaves that may be produced in large quantities from stems of silvery-thread moss.